JavaScript for loop check condition and executes block of code for a specific number of times, until specified condition argument become false.
JavaScript for loop accept 3 arguments separated by semicolons. All 3 arguments are optional.
Syntax
for (initialization; condition; iteration) {
statements; // Do stuff if for loop condition is true
}
Arguments
- initialization: var keyword to define and initialize counter variable. you can initializes the values of one or more counter variables. One or more counter variables separated by colon.
- condition: Check the condition expression, for given condition true or not. If the condition true, execute the block of code otherwise terminates the for loop.
- iteration: last end of loop iteration counter variable are evaluated. Here you can specify step of increment/decrement, default one.
Example: Following for loop example execute block of code until
num value become 10. When num value become 11 the condition no longer satisfy and finally skip to execute for block.<script>
for( var num = 1; num <= 10; num++ ){
document.writeln(num + ": iteration");
}
document.writeln("End of for loop");
</script>
Example Result
Array iteration in for loop
Example 1 :
<script>
var arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
for ( var num = 0; num < arr.length; num ++ ) {
document.writeln(num + " iterate");
}
document.writeln("End of array for loop");
</script>
Example Result :
Example 2: we can little optimization for loop, length of the array store in variable and avoid to calculating length of array every iteration.
<script>
var arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
for ( var num = 0, size = arr.length; num < size; num++ ) {
document.writeln(num + " iterate");
}
document.writeln("End of array for loop");
</script>
Example Result
For loop arguments: optional
JavaScript for loop all three arguments are as an optional. Let's see one bye one without specified optional arguments,
Example 1 : Initialization arguments are as an optional.
<script>
var num = 1;
for(; num <= 10; num++){
document.writeln(num + ": iteration");
}
document.writeln("End of for loop");
</script>
Example Result :
Example 2: Condition arguments are as an optional.
break; keyword indicates to terminate for loop condition.<script>
var num = 1;
for(; ; num++){
if (num <= 10)
document.writeln(num + ": iteration");
else
break;
}
document.writeln("End of for loop");
</script>
Example Result
Example 3: last iteration arguments are as an optional.
<script>
var num = 1;
for( ; ; ){
if (num <= 10)
document.writeln(num + ": iteration");
else
break;
num++;
}
document.writeln("End of for loop");
</script>
Example Result
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