Control Flow

While Loop in JavaScript

The while loop executes a block of code while a boolean expression evaluates to true. It terminates as soon as the expression evaluates to false. The boolean expression is evaluated before each iteration.

Syntax

while(booleanExpression) { 
    //block of code to be executed
}

Notes

Because the boolean expression is evaluated before each iteration, the block of code executes ONLY if the booleanExpression evaluates to true. If a guarantee is needed for the block of code to run at least once, use the do-while loop.

booleanExpression results in either a true or false output. It is created using comparing operators (==, >, =, <=, !=).

There can also be multiple boolean expressions within the parentheses (booleanExpression). The boolean expressions are connected through logical operators (&&, ||, !).

Example

var x = 0; 
while(x < 10) { 
    console.log(x); //prints x until x < 10 evaluates to false
x++; 
}

See Also

while - JavaScript | MDN