Tutorials References Exercises Videos Menu
Create Website Get Certified Upgrade


JS Reference

JS by Category JS by Alphabet

JavaScript

JS Array JS Boolean JS Classes JS Date JS Error JS Global JS JSON JS Math JS Number JS Object JS Operators JS Precedence JS RegExp JS Statements JS String JS TypedArray

Window

Window Object Window Console Window History Window Location Window Navigator Window Screen

HTML DOM

HTML Documents HTML Elements HTML Attributes HTML Collection HTML NodeList HTML DOMTokenList HTML Styles
alignContent alignItems alignSelf animation animationDelay animationDirection animationDuration animationFillMode animationIterationCount animationName animationTimingFunction animationPlayState background backgroundAttachment backgroundClip backgroundColor backgroundImage backgroundOrigin backgroundPosition backgroundRepeat backgroundSize backfaceVisibility border borderBottom borderBottomColor borderBottomLeftRadius borderBottomRightRadius borderBottomStyle borderBottomWidth borderCollapse borderColor borderImage borderImageOutset borderImageRepeat borderImageSlice borderImageSource borderImageWidth borderLeft borderLeftColor borderLeftStyle borderLeftWidth borderRadius borderRight borderRightColor borderRightStyle borderRightWidth borderSpacing borderStyle borderTop borderTopColor borderTopLeftRadius borderTopRightRadius borderTopStyle borderTopWidth borderWidth bottom boxShadow boxSizing captionSide caretColor clear clip color columnCount columnFill columnGap columnRule columnRuleColor columnRuleStyle columnRuleWidth columns columnSpan columnWidth counterIncrement counterReset cssFloat cursor direction display emptyCells filter flex flexBasis flexDirection flexFlow flexGrow flexShrink flexWrap font fontFamily fontSize fontStyle fontVariant fontWeight fontSizeAdjust height isolation justifyContent left letterSpacing lineHeight listStyle listStyleImage listStylePosition listStyleType margin marginBottom marginLeft marginRight marginTop maxHeight maxWidth minHeight minWidth objectFit objectPosition opacity order orphans outline outlineColor outlineOffset outlineStyle outlineWidth overflow overflowX overflowY padding paddingBottom paddingLeft paddingRight paddingTop pageBreakAfter pageBreakBefore pageBreakInside perspective perspectiveOrigin position quotes resize right scrollBehavior tableLayout tabSize textAlign textAlignLast textDecoration textDecorationColor textDecorationLine textDecorationStyle textIndent textOverflow textShadow textTransform top transform transformOrigin transformStyle transition transitionProperty transitionDuration transitionTimingFunction transitionDelay unicodeBidi userSelect verticalAlign visibility width wordBreak wordSpacing wordWrap widows zIndex

HTML Events

HTML Events HTML Event Objects

Web APIs

API Console API Fetch API Fullscreen API Geolocation API History API MediaQueryList API Storage API Validation API Web

HTML Objects

<a> <abbr> <address> <area> <article> <aside> <audio> <b> <base> <bdo> <blockquote> <body> <br> <button> <canvas> <caption> <cite> <code> <col> <colgroup> <datalist> <dd> <del> <details> <dfn> <dialog> <div> <dl> <dt> <em> <embed> <fieldset> <figcaption> <figure> <footer> <form> <head> <header> <h1> - <h6> <hr> <html> <i> <iframe> <img> <ins> <input> button <input> checkbox <input> color <input> date <input> datetime <input> datetime-local <input> email <input> file <input> hidden <input> image <input> month <input> number <input> password <input> radio <input> range <input> reset <input> search <input> submit <input> text <input> time <input> url <input> week <kbd> <label> <legend> <li> <link> <map> <mark> <menu> <menuitem> <meta> <meter> <nav> <object> <ol> <optgroup> <option> <output> <p> <param> <pre> <progress> <q> <s> <samp> <script> <section> <select> <small> <source> <span> <strong> <style> <sub> <summary> <sup> <table> <tbody> <td> <tfoot> <th> <thead> <tr> <textarea> <time> <title> <track> <u> <ul> <var> <video>

Other References

CSSStyleDeclaration JS Conversion


JavaScript for Loop

Example

Loop (iterate over) a code block five times:

for (let i = 0; i < 5; i++) {
  text += i + "<br>";
}
Try it Yourself »

Loop (iterate over) an array to collect car names:

const cars = ["BMW", "Volvo", "Saab", "Ford"];
for (let i = 0; i < cars.length; i++) {
  text += cars[i] + "<br>";
}
Try it Yourself »
  • The loop starts in position 0 (let i = 0).
  • The loop automatically increments i for each run.
  • The loop runs as long as i < cars.length.

More examples below.


Definition and Usage

The for statement defines a code block that is executed as long as a condition is true.

Note

If you omit statement 2, you must provide a break inside the loop.

Otherwise the loop will never end. This will crash your browser.

See Also:

The JavaScript for Tutorial


Syntax

for (statement 1; statement 2; statement 3) {
  code block to be executed
}

Parameters

Parameter Description
statement 1 Optional.
Executed before the code block starts.
Normally used to initialize a counter variable.
To initiate multiple values, separate each value with a comma.

This parameter can be omitted, but not the semicolon ";"
statement 2 Optional.
The condition for running the code block.
If it returns true the loop will start over again, otherwise the loop will end.

This parameter can be omitted, but not the semicolon ";"
statement 3 Optional.
Executed after the code block.
Normally used to increment the counter variable.

This parameter can be omitted (e.g. to increase/decrease values inside the loop)

JavaScript Loop Statements

StatementDescription
breakBreaks out of a loop
continueSkips a value in a loop
whileLoops a code block while a condition is true
do...whileLoops a code block once, and then while a condition is true
forLoops a code block while a condition is true
for...ofLoops the values of any iterable
for...inLoops the properties of an object


More Examples

Initiate multiple values in the first parameter:

const cars = ["BMW", "Volvo", "Saab", "Ford"];
for (let i = 0, len = cars.length, text = ""; i < len; i++) {
  text += cars[i] + "<br>";
}
Try it Yourself »

Omit the first parameters (set the values before the loop starts):

const cars = ["BMW", "Volvo", "Saab", "Ford"];
let i = 2;
let len = cars.length;
let text = "";
for (; i < len; i++) {
  text += cars[i] + "<br>";
}
Try it Yourself »

Use continue - Loop through a block of code, but skip the value 3:

let text = "";
for (let i = 0; i < 5; i++) {
  if (i == 3) continue;
  text += i + "<br>";
}
Try it Yourself »

Use break - Loop a code block, but exit the loop when i == 3:

let text = "";
for (let i = 0; i < 5; i++) {
  if (i == 3) break;
  text += i + "<br>";
}
Try it Yourself »

Omit the second parameter.

Use break to exit the loop, otherwise the loop will never end, and your browser will crash:

const cars = ["BMW", "Volvo", "Saab", "Ford"];
let text = "";
for (let i = 0; ; i++) {
  if (i == cars-length) break;
  text += cars[i] + "<br>";
}
Try it Yourself »

Loop over an array in descending order (negative increment):

const cars = ["BMW", "Volvo", "Saab", "Ford"];
let text = "";
for (let i = cars.length - 1; i >= 0; i--) {
  text += cars[i] + "<br>";
}
Try it Yourself »

Omit the last parameter, and increment the values inside the loop:

const cars = ["BMW", "Volvo", "Saab", "Ford"];
let i = 0;
let len = cars.length;
for (; i < len;) {
  text += cars[i] + "<br>";
  i++;
}
Try it Yourself »

Loop a NodeList and change the color of all p elements in the list:

const myNodelist = document.getElementsByTagName("P");
for (let i = 0; i < myNodelist.length; i++) {
  myNodelist[i].style.color = "blue";
}
Try it Yourself »

A nested loop (a loop inside a loop):

let text = "";
for (let = 0; i < 3; i++) {
  text += i + "<br>";
  for (let j = 10; j < 15; j++) {
    text += j + "<br>";
  }
}
Try it Yourself »

Browser Support

for is an ECMAScript1 (ES1) feature.

ES1 (JavaScript 1997) is fully supported in all browsers:

Chrome Edge Firefox Safari Opera IE
Yes Yes Yes Yes Yes Yes