Tutorials References Exercises Bootcamps Videos Menu
Sign Up Create Website Get Certified Upgrade

JS Reference

JS by Category JS by Alphabet


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 Object Window Console Window History Window Location Window Navigator Window Screen


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 HTML Event Properties HTML Event Methods

Web APIs

API Canvas 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 Array reduce()


Subtract all numbers in an array:

const numbers = [175, 50, 25];

document.getElementById("demo").innerHTML = numbers.reduce(myFunc);

function myFunc(total, num) {
  return total - num;
Try it Yourself »

Round all the numbers and display the sum:

const numbers = [15.5, 2.3, 1.1, 4.7];
document.getElementById("demo").innerHTML = numbers.reduce(getSum, 0);

function getSum(total, num) {
  return total + Math.round(num);
Try it Yourself »


The reduce() method executes a reducer function for array element.

The reduce() method returns a single value: the function's accumulated result.

The reduce() method does not execute the function for empty array elements.

The reduce() method does not change the original array.


At the first callback, there is no return value from the previous callback.

Normally, array element 0 is used as initial value, and the iteration starts from array element 1.

If an initial value is supplied, this is used, and the iteration starts from array element 0.

See Also:

The Array reduceRight() Method


array.reduce(function(total, currentValue, currentIndex, arr), initialValue)


Parameter Description
function() Required.
A function to be run for each element in the array.
Reducer function parameters:
total Required.
The initialValue, or the previously returned value of the function.
currentValue Required.
The value of the current element.
currentIndex Optional.
The index of the current element.
arr Optional.
The array the current element belongs to.
initialValue Optional.
A value to be passed to the function as the initial value.

Return Value

The accumulated result from the last call of the callback function.

Browser Support

reduce() is an ECMAScript5 (ES5) feature.

ES5 (JavaScript 2009) fully supported in all browsers:

Chrome Edge Firefox Safari Opera IE
Yes Yes Yes Yes Yes 9-11