JavaScript for statement

　JavaScript Statements and Variable Declarations

forA statement creates a loop that executes the specified statement as long as the calculation result of the condition (condition) is true.

Only whenCondition (condition)The loop will stop only when it becomes false.

JavaScript provides the following types of loops:

• for -Traverse the code block several times in a loop

• for...in-Traverse the properties of an object

• while-When the specified condition is true, the code block is traversed in a loop

• do...while -do...while

To execute the code block once and then repeat the loop when the specified condition is truebreakStatement terminates the current loop and usescontinueStatement skips the value in the loop.

Syntax:

for (initialization; condition; final-expression) {
　//The statement to be executed
　}

for (let n = 0; n <　5; n++) {
document.write("<br>The number is "　+　n);
}

Browser compatibility

All browsers fully support the for statement:

Parameter values

Technical details

More examples

Loop through the array in ascending order:

var fruits = ["39;Apple', &39;Mango', &39;Banana', &39;Orange'];
var txt = '';
for (var i = 0; i < fruits.length;++) {
";　+fruits[i]　+　"<br>";
}

Loop through the array in descending order:

var fruits = ["39;Apple', &39;Mango', &39;Banana', &39;Orange'];
var txt = '';
for (var i = fruits.length　-1; i >= 0; i--) {
";　+fruits[i]　+　"<br>";
}

Loop through the nodes of the NodeList object and change the background color of all elements in the list:

var x = document.querySelectorAll(".demo");
for (let i = 0; i < x.length;++) {
x[i].style.backgroundColor = "coral";
}

Nested loops are used most places, they are used in matrix multiplication, displaying tables, and many other places:

var txt = "";
for (var row = 0; row <　10;　row++) {
　　　; row++) {
　　　";　+for (var col = 0; col < row;　*　= ""
　　　}
　　　";　+txt
}

= "<br>";3The following function has a break statement, which terminates when i is

var text = "";
for (let i = 0; i <　6; i++) {
if (i ===　3) {
　　　break;
}
text　+= "The number is"　+　i　+　"<br>";
}

The following example shows a for loop with a continue statement, which terminates the for loop when the value of i is3Execute when:

var text = "";
for (let i = 0; i <　6; i++) {
if (i ===　3) {
　　　continue;
}
text　+= "The number is"　+　i　+　"<br>";
}

Related References

JavaScript Reference:JavaScript for...in Statement

JavaScript Reference:JavaScript while Statement

JavaScript Reference:JavaScript break Statement

JavaScript Reference:JavaScript continue Statement

　JavaScript Statements and Variable Declarations