Underscore.js Introduction (original) (raw)

Last Updated : 29 Nov, 2021

Underscore.js is a lightweight JavaScript library and not a complete framework that was written by Jeremy Ashkenas that provides utility functions for a variety of use cases in our day to day common programming tasks.

With just under six kilobytes in size, this library basically provides us with a whole bunch of useful JavaScript functions for making our life easier, there are literally hundreds of different functions available that support both our workaday functional helpers such as the map and filter functions, as well as more specialized ones such as JavaScript templating, function binding, deep equality testing, creating quick indexes, and many more.

Underscore functions basically falls under four major categories which are functions that can be used for manipulating arrays, functions that can be used for manipulating objects, functions that can be used for manipulating both arrays as well as objects and functions that can be used for manipulating other functions itself.

Features of Underscore:

• Perform common operations of data like arrays, objects, JSON files etc.
• Compatible with other JS libraries like jQuery to perform DOM operation.
• Contains function for data manipulation.

Kinds of Data Operation:

• Fetch Data from Collection.
• Transform Data in various formats.
• Sort, Filter and Group Data.
• Convert Data into Required result by performing specific operation on them.
• Templates can be used to perform data operations.

Installation:

• Node.js:

npm install underscore

• Meteor.js:

meteor add underscore

• Require.js:

require(["underscore"], ...

• Bower:

bower install underscore

• ExtendScript:

#include "underscore.js"

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Underscore.js Collections Functions

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Underscore.js Arrays Functions

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• Underscore.js _.last() Function Underscore.js _.last() is used to display the last element of the array. It is usually applied to separate the elements of an array by making it into 2 arrays. One which contains only the last element and the other which contains all the elements except the last one. Syntax:_.last( array, [n] ) Para 3 min read

• Underscore.js _.rest() Function The Underscore.js is a JavaScript library that provides a lot of useful functions like the map, filter, invoke etc even without using any built-in objects. The _.rest() is used to return the rest of the elements except the zeroth indexed element. Second parameter is used to start the search from the 3 min read

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• Underscore.js _.without() Function Underscore.js _.without() function is used to return a copy of the array which contains all the array except values. Syntax:_.without( array, *values );Parameters:array: This parameter is used to hold the list of array elements.values: This parameter is used to hold the value that needs to be remove 3 min read

• Underscore.js _.union() Function Underscore.js _.union() function is used to take n number of arrays and return a new array with the unique terms in all those arrays (union of all array). In the new array, the order of the elements is the same as it is mentioned in all the passed arrays. The first occurrence of each array is only i 3 min read

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• Underscore.js _.difference() Function Underscore.js _.difference() function returns the values of the array that are not present in the other arrays. If the element is present in the array then this element will not be included in the resultant array. This is because it takes a difference between the second array and the first array. Sy 3 min read

• Underscore.js _.uniq() Function Underscore.js _.uniq() function returns the array which does not contain duplicate elements. The first occurrence of the element is included in the resultant array. The operation of checking whether the array is duplicate or not. It is done by the '===' operation. Syntax:_.uniq( array, [isSorted], 3 min read

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Underscore.js Functions

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• Underscore.js _.partial() Function The _.partial() function is used to apply partially a function by filling in any number of its arguments, without changing its dynamic value. Syntax: _.partial(function, *arguments) Parameters: This function accept two parameters as mentioned above and described below: function: The function that ne 1 min read

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• Underscore.js _.delay() Function Underscore.js _.delay() function executes the mentioned function in its argument after waiting for the specified milliseconds. It is mostly used when we want to perform some task but after a certain amount of time. In this case, we can define this function, and then it will be executed after the wai 4 min read

• Underscore.js _.defer() Function Underscore.js _.defer() function is used to invoke/call a function until the current call stack is cleared. Its major advantage is that it performs expensive computations, calculations, or HTML in chunks without blocking the UI threads from updating. It has a similar functioning to the setTimeOut() 3 min read

• Underscore.js _.once() Function Underscore.js _.once function is used in conditions where we want a particular function to be executed only a single time. Even though we execute or call this function multiple times then also it will have no effect. The original function's values will only be returned each time it is called. It is 5 min read

• Underscore.js _.after() Function Underscore.js is a JavaScript library that provides a lot of useful functions that help in the programming in a big way like the map, filter, invoke, etc even without using any built-in objects. The _.after() function is an inbuilt function in Underscore.js library of JavaScript which is used to cre 2 min read

• Underscore.js _.before() Function _.before() function in underscore.js is used to call a particular function a particular number of times. It uses a count variable that keeps the track of number of times the function is called. Syntax: _.before(count, function) Parameters: Count: It is the number of times a function is to be called. 2 min read

• Underscore.js _.wrap() Function Underscore.js _.wrap() is used to wrap a function inside another function. It means that the first calling function will be invoked first and then the called function will be executed. If the calling function does not call the called function then the second function will not be executed. Syntax:_.w 3 min read

• Underscore.js _.negate() Function Underscore.js is a JavaScript library that provides a lot of useful functions that help in the programming in a big way like the map, filter, invoke, etc even without using any built-in objects. The _.negate() function is an inbuilt function in Underscore.js library of JavaScript which is used to fi 1 min read

• Underscore.js _.compose() Function The _.compose() function is used to return the composition of the list of functions. The list of the function returns the value of the function that follows. Syntax: _.compose(*functions) Parameters: This function accept a single parameter as mentioned above and described below: functions: It contai 1 min read

• Underscore.js _.restArguments() Function Underscore.js is a JavaScript library that provides a lot of useful functions that help in the programming in a big way like the map, filter, invoke, etc. even without using any built-in objects. The _.restArguments() function is an inbuilt function in Underscore.js library of JavaScript which is us 2 min read

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Underscore.js Object Functions

• Underscore.js _.keys() Function Underscore.js_.keys() function is used to return the list of all keys of the given object. Syntax:_.keys( object );Parameters:object: It contains the object elements.Return Value: This function returns the list of all keys of the given object. Example 1: This example shows the use of the _.keys() fu 1 min read

• Underscore.js _.allKeys() Function The _.allKeys() function is used to return all keys of the object and inherited properties. Syntax: _.allKeys( object ) Parameters: This function accept oa single parameter as mentioned above and described below: object: It contains the object element that holds the elements of key and value pair. R 1 min read

• Underscore.js _.values() Function The _.values() function is used to return the list of all values of the object element. Syntax: _.values( object ) Parameters: This function accepts one parameter as mentioned above and described below: object: It contains the object element that holds the elements of key and value pair. Return Valu 1 min read

• Underscore.js _.mapObject() Function The _.mapObject() function is similar to the map but used for the object. This function transforms each value of the object based on the given function/operation. Syntax: _.mapObject(object, iteratee, [context]) Parameters: This function accepts three parameters as mentioned above and described belo 1 min read

• Underscore.js _.pairs() Function Underscore.js _.pairs() function is used to convert an object into an array of arrays that contain the [key, value] pairs of the object as elements. Syntax:_.pairs( object );Parameters:object: It contains the object element that holds the elements of key and value pair.Return Value:It returns the ar 1 min read

• Underscore.js _.invert() Function Underscore.js _.invert() function is used to return the copy of an object where the object key is converted into value and object value is converted into the key. It means the [key, value] of the object is reversed. Syntax:_.invert( object );Parameters:object: It contains the object element that hol 1 min read

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• Underscore.js _.functions() Function Underscore.js _.functions() function is used to return the sorted list of all methods that are present in an object. Syntax:_.functions(object);Parameters: object: It contains the object element that holds the elements [key, value] pair.Return Value: It returns the sorted list of all methods that ar 1 min read

• Underscore.js _.findKey() Function The _.findKey() function is used to return the key value where the predicate logic or condition returns the truth value or undefined. The predicate function/condition is transformed through iteratee to facilitate shorthand syntaxes. Syntax: _.findKey(object, predicate, [context]) Parameters: This fu 1 min read

• Underscore.js _.extend() Function Underscore.js _.extend() function is used to create a copy of all of the properties of the source objects over the destination object and return the destination object. The nested arrays or objects will be copied by using reference, not duplicated. Syntax:_.extend(destination, *sources);Parameters: 1 min read

• Underscore.js _.extendOwn() Function The _.extendOwn() function is used to copy only own properties over to the destination object. This function is similar to the _.extend() function. Syntax: _.extendOwn(destination, *sources) Parameters: This function accept two parameters as mentioned above and described below: destination: This par 1 min read

• Underscore.js _.pick() Function Underscore.js _.pick() function is used to return a copy of the object that is filtered using the given key. This function accepts a predicate indicating which keys are picked from the object. Syntax:_.pick(object, *keys);Parameters: object: This parameter holds the value of an object.keys: It is an 1 min read

• Underscore.js _.omit() Function Underscore.js _.omit() function is used to return a copy of the object that was filtered to omit the blacklisted keys. Syntax:_.omit(object, *keys);Parameters:object: This parameter holds the value of an object.keys: It is an optional parameter. It contains the key name that the value needs to be om 1 min read

• Underscore.js _.defaults() Function Underscore.js _.defaults() function returns the object after filling in its undefined properties with the first value present in the following list of default objects. Syntax:_.defaults(object, *defaults);Parameters:object: This parameter holds the value of an object.defaults: It is an optional para 1 min read

• Underscore.js Objects Complete Reference Underscore provides a number of common object related methods such as the key and values functions. These functions are used to return the list of all keys and value of the given object respectively . All the underscore objects examples are given below with their references: Function Description _.k 3 min read

Underscore.js Utility Functions

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• Underscore.js _.identity() Function Underscore.js is a JavaScript library that makes operations on arrays, string, objects much easier and handy. The _.identity() function is used to return the exact same replica of the value given to it as the argument. This function looks useless, but is used throughout Underscore as a default itera 2 min read

• Underscore.js _.constant() Function Underscore.js is a JavaScript library that makes operations on arrays, string, objects much easier and handy. The _.constant() function is used to create a function that returns the parameter given to it. It is almost same as _.identity() function. Note: It is very necessary to link the underscore C 2 min read

• Underscore.js _.noop() Function Underscore.js is a JavaScript library that makes operations on arrays, string, objects much easier and handy. The _.noop() function is used to return "undefined" irrespective of the arguments passed to it. Note: It is very necessary to link the underscore CDN before going and using underscore functi 2 min read

• Underscore.js _.times() Function Underscore.js _.times() function is used to call the function a particular number of times i.e. execution of a function(f) "n" times. NOTE: It is very necessary to link the underscore CDN before going and using the underscore functions in the browser. When linking the underscore.js CDN link, the "_" 2 min read

• Underscore.js _.random() Function Underscore.js is a library in javascript that makes operations on arrays, string, objects much easier and handy. The _.random() function is used to return a random integer which is in the range provided to the function. Note: It is very necessary to link the underscore CDN before going and using und 2 min read

• Underscore.js _.mixin() Function Underscore.js is a JavaScript library that makes operations on arrays, string, objects much easier and handy. The _.mixin() function is used to add extra functionality and extend the global underscore object to some special utility functions. Its important to link the underscore CDN before going and 2 min read

• Underscore.js _.iteratee() Function Underscore.js is a JavaScript library that provides a lot of useful functions that help in the programming in a big way like the map, filter, invoke, etc. even without using any built-in objects. The _.iteratee() function is an inbuilt function in Underscore which is used to generate a callback that 2 min read

• Underscore.js _.uniqueId() Function Underscore.js is a JavaScript library that provides a lot of useful functions that help in the programming in a big way like the map, filter, invoke, etc even without using any built-in objects. The _.uniqueId() function is an inbuilt function in Underscore.js library of JavaScript which is used to 2 min read

• Underscore.js _.escape() function Underscore.js _.escape() function is used to escape a special character string from inserting into HTML. Some of the strings that get escape are "&", ">", "<", "''", etc. Note: Some special files are needed to be included while using this code directly in the browser. It is very necessary 1 min read

• Underscore.js _.unescape() function Underscore.js is a library in javascript that makes operations on arrays, string, objects much easier and handy. _.unescape() function is used to unescape a special character. It works opposite of _.escape() function. It do convert "&" to "&" and so on. Syntax: _.unescape(string); Parame 1 min read

• Underscore.js _.result() Function Underscore.js is a JavaScript library that provides a lot of useful functions that helps in the programming in a big way like the map, filter, invoke etc even without using any built-in objects. The _.result() function is an inbuilt function in Underscore.js library of JavaScript. Here, if the state 2 min read

• Underscore.js _.now() function Underscore.js is a library in javascript that makes operations on arrays, string, objects much easier and handy. _.now() function is used to return the timestamp of the current time. This method can be useful when working with animations in the browser. Syntax: _.now(); Parameters: It takes no param 1 min read

• Underscore.js Utility Complete Reference Underscore.js is a lightweight JavaScript library and not a complete framework that was written by Jeremy Ashkenas that provides utility functions for a variety of use cases in our day-to-day common programming tasks. The complete reference for underscore utility is provided below: Function Descript 2 min read

Underscore.js Questions

• How to use if statements in Underscore.js templates ? Underscore.js is a javascript library that provides helper functions in functional programming without extending the built-in objects. This package consists of 100 functions like map, filter, etc. We can install this by using npm. npm install underscore Syntax: const _ = require('underscore'); Appro 1 min read

• Difference between lodash and Underscore The lodash and UnderScore both are utility libraries from JavaScript which helps make it easier by providing utils which makes, working with arrays, numbers, objects, and strings much easier. They provide a group of tools used for common programming operations having a strong functional programming 3 min read

• How to break _.each() function in Underscore.js ? It is not possible to break the _.each function. The reason is that the _.each function works similarly to the forEach function and imitates its native behavior. It does not allow us to break the loop or escape from it except by throwing an exception. However, one can use different methods like: Thr 2 min read

• How to use underscore.js as a template engine ? While writing layouts for web pages, it is often the case that we require certain elements of the page to have dynamic values. For such scenarios, we use templates. Templates enable us to embed logical segments inside static HTML code, which makes the page dynamic based on the values passed in the t 3 min read

• How to deep flatten an array in JavaScript? In this article, we will learn how to deep flatten an array in JavaScript. The flattening of an array is a process of merging a group of nested arrays present inside a given array. Deep flattening means that the array would be completely flattened. Example: Input: [1,2,3,4,5,[6,[7,8,9]]] Output: [1, 2 min read