JavaScript ifelse (original) (raw)
JavaScript if-else
Last Updated : 31 May, 2024
**JavaScript if-else statement executes a block of code based on a condition. If the condition evaluates to true, the code inside the “if” block executes; otherwise, the code inside the “else” block, if present, executes.
Such control statements are used to cause the flow of execution to advance and branch based on changes to the state of a program.
**Example: This example describes the if-statement in JavaScript.
JavaScript `
// JavaScript program to illustrate If statement let i = 10;
if (i > 15) console.log("10 is less than 15");
// This statement will be executed // as if considers one statement by default console.log("I am Not in if");
`
**JavaScript’s conditional statements
Table of Content
- JavaScript if-statement
- JavaScript if-else statement
- JavaScript nested-if statement
- JavaScript if-else-if ladder statement
We will understand each conditional statement, its syntax, flowchart, and examples. Please refer to the Switch Case in JavaScript article to understand the switch case. Let’s begin with the if-statement.
**JavaScript if-statement
It is a conditional statement used to decide whether a certain statement or block of statements will be executed or not i.e. if a certain condition is true then a block of statements is executed otherwise not.
**Syntax:
if(condition)
{
// Statements to execute if
// condition is true
}
The if statement accepts boolean values – if the value is true then it will execute the block of statements under it. If we do not provide the curly braces ‘{‘ and ‘}’ after **if( condition ) then by default if statement considers the immediate one statement to be inside its block. For example,
if(condition)
statement1;
statement2;
// Here if the condition is true, if block
// will consider only statement1 to be inside
// its block.
**Flow chart:
if-condition statement
**Example: Here is a simple example demonstrating the **if statement.
JavaScript `
// JavaScript program to illustrate If statement let age = 19;
if (age > 18) console.log("Congratulations, You are eligible to drive");
`
Output
Congratulations, You are eligible to drive
**JavaScript if-else statement
The if statement alone tells us that if a condition is true it will execute a block of statements and if the condition is false it won’t. But what if we want to do something else if the condition is false? Here comes the else statement. We can use the else statement with the if statement to execute a block of code when the condition is false.
**Syntax:
if (condition)
{
// Executes this block if
// condition is true
}
else
{
// Executes this block if
// condition is false
}
**Flow chart:
if-else statement
**Example: This example describes the if-else statement in Javascript.
JavaScript `
// JavaScript program to illustrate If-else statement let i = 10;
if (i < 15) console.log("i is less than 15"); else console.log("I am Not in if");
`
**JavaScript nested-if statement
JavaScript allows us to nest if statements within if statements. i.e, we can place an if statement inside another if statement. A nested if is an if statement that is the target of another if or else.
**Syntax:
if (condition1)
{
// Executes when condition1 is true
if (condition2)
{
// Executes when condition2 is true
}
}
**Flow chart:
nested-if statement
**Example: This example describes the nested-if statement in Javascript.
JavaScript `
// JavaScript program to illustrate nested-if statement let i = 10;
if (i == 10) { // First if statement if (i < 15) { console.log("i is smaller than 15"); // Nested - if statement // Will only be executed if statement above // it is true if (i < 12) console.log("i is smaller than 12 too"); else console.log("i is greater than 15"); } }
`
Output
i is smaller than 15 i is smaller than 12 too
**JavaScript if-else-if ladder statement
Here, a user can decide among multiple options. The if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
**Syntax:
if (condition)
statement;
else if (condition)
statement;
.
.
else
statement;
**Flow chart:
if-else-if ladder statement
**Example: This example describes the if-else-if ladder statement in Javascript.
JavaScript `
// JavaScript program to illustrate nested-if statement let i = 20;
if (i == 10) console.log("i is 10"); else if (i == 15) console.log("i is 15"); else if (i == 20) console.log("i is 20"); else console.log("i is not present");
`