DOM Elements

React implements a browser-independent DOM system for performance and cross-browser compatibility. We took the opportunity to clean up a few rough edges in browser DOM implementations.

In React, all DOM properties and attributes (including event handlers) should be camelCased. For example, the HTML attribute tabindex corresponds to the attribute tabIndex in React. The exception is aria-* and data-* attributes, which should be lowercased. For example, you can keep aria-label as aria-label.

Differences In Attributes

There are a number of attributes that work differently between React and HTML:

checked

The checked attribute is supported by <input> components of type checkbox or radio. You can use it to set whether the component is checked. This is useful for building controlled components. defaultChecked is the uncontrolled equivalent, which sets whether the component is checked when it is first mounted.

className

To specify a CSS class, use the className attribute. This applies to all regular DOM and SVG elements like <div>, <a>, and others.

If you use React with Web Components (which is uncommon), use the class attribute instead.

dangerouslySetInnerHTML

dangerouslySetInnerHTML is React’s replacement for using innerHTML in the browser DOM. In general, setting HTML from code is risky because it’s easy to inadvertently expose your users to a cross-site scripting (XSS) attack. So, you can set HTML directly from React, but you have to type out dangerouslySetInnerHTML and pass an object with a __html key, to remind yourself that it’s dangerous. For example:

function createMarkup() {
  return {__html: 'First &middot; Second'};
}

function MyComponent() {
  return <div dangerouslySetInnerHTML={createMarkup()} />;
}

htmlFor

Since for is a reserved word in JavaScript, React elements use htmlFor instead.

onChange

The onChange event behaves as you would expect it to: whenever a form field is changed, this event is fired. We intentionally do not use the existing browser behavior because onChange is a misnomer for its behavior and React relies on this event to handle user input in real time.

selected

The selected attribute is supported by <option> components. You can use it to set whether the component is selected. This is useful for building controlled components.

style

The style attribute accepts a JavaScript object with camelCased properties rather than a CSS string. This is consistent with the DOM style JavaScript property, is more efficient, and prevents XSS security holes. For example:

const divStyle = {
  color: 'blue',
  backgroundImage: 'url(' + imgUrl + ')',
};

function HelloWorldComponent() {
  return <div style={divStyle}>Hello World!</div>;
}

Note that styles are not autoprefixed. To support older browsers, you need to supply corresponding style properties:

const divStyle = {
  WebkitTransition: 'all', // note the capital 'W' here
  msTransition: 'all' // 'ms' is the only lowercase vendor prefix
};

function ComponentWithTransition() {
  return <div style={divStyle}>This should work cross-browser</div>;
}

Style keys are camelCased in order to be consistent with accessing the properties on DOM nodes from JS (e.g. node.style.backgroundImage). Vendor prefixes other than ms should begin with a capital letter. This is why WebkitTransition has an uppercase “W”.

React will automatically append a “px” suffix to certain inline style properties. For example:

// This:
<div style={{ height: 10 }}>
  Hello World!
</div>;

// Becomes:
<div style="height: 10px;">
  Hello World!
</div>

Not all style properties are converted to pixel strings though. Certain ones remain unitless (eg zoom, order, flex). A complete list of unitless properties can be seen here.

suppressContentEditableWarning

Normally, there is a warning when an element with children is also marked as contentEditable, because it won’t work. This attribute suppresses that warning. Don’t use this unless you are building a library like Draft.js that manages contentEditable manually.

value

The value attribute is supported by <input> and <textarea> components. You can use it to set the value of the component. This is useful for building controlled components. defaultValue is the uncontrolled equivalent, which sets the value of the component when it is first mounted.

All Supported HTML Attributes

As of React 16, any standard or custom DOM attributes are fully supported.

React has always provided a JavaScript-centric API to the DOM. Since React components often take both custom and DOM-related props, React uses the camelCase convention just like the DOM APIs:

<div tabIndex="-1" />      // Just like node.tabIndex DOM API
<div className="Button" /> // Just like node.className DOM API
<input readOnly={true} />  // Just like node.readOnly DOM API

These props work similarly to the corresponding HTML attributes, with the exception of the special cases documented above.

Some of the DOM attributes supported by React include:

accept acceptCharset accessKey action allowFullScreen allowTransparency alt
async autoComplete autoFocus autoPlay capture cellPadding cellSpacing challenge
charSet checked cite classID className colSpan cols content contentEditable
contextMenu controls controlsList coords crossOrigin data dateTime default defer
dir disabled download draggable encType form formAction formEncType formMethod
formNoValidate formTarget frameBorder headers height hidden high href hrefLang
htmlFor httpEquiv icon id inputMode integrity is keyParams keyType kind label
lang list loop low manifest marginHeight marginWidth max maxLength media
mediaGroup method min minLength multiple muted name noValidate nonce open
optimum pattern placeholder poster preload profile radioGroup readOnly rel
required reversed role rowSpan rows sandbox scope scoped scrolling seamless
selected shape size sizes span spellCheck src srcDoc srcLang srcSet start step
style summary tabIndex target title type useMap value width wmode wrap

Similarly, all SVG attributes are fully supported:

accentHeight accumulate additive alignmentBaseline allowReorder alphabetic
amplitude arabicForm ascent attributeName attributeType autoReverse azimuth
baseFrequency baseProfile baselineShift bbox begin bias by calcMode capHeight
clip clipPath clipPathUnits clipRule colorInterpolation
colorInterpolationFilters colorProfile colorRendering contentScriptType
contentStyleType cursor cx cy d decelerate descent diffuseConstant direction
display divisor dominantBaseline dur dx dy edgeMode elevation enableBackground
end exponent externalResourcesRequired fill fillOpacity fillRule filter
filterRes filterUnits floodColor floodOpacity focusable fontFamily fontSize
fontSizeAdjust fontStretch fontStyle fontVariant fontWeight format from fx fy
g1 g2 glyphName glyphOrientationHorizontal glyphOrientationVertical glyphRef
gradientTransform gradientUnits hanging horizAdvX horizOriginX ideographic
imageRendering in in2 intercept k k1 k2 k3 k4 kernelMatrix kernelUnitLength
kerning keyPoints keySplines keyTimes lengthAdjust letterSpacing lightingColor
limitingConeAngle local markerEnd markerHeight markerMid markerStart
markerUnits markerWidth mask maskContentUnits maskUnits mathematical mode
numOctaves offset opacity operator order orient orientation origin overflow
overlinePosition overlineThickness paintOrder panose1 pathLength
patternContentUnits patternTransform patternUnits pointerEvents points
pointsAtX pointsAtY pointsAtZ preserveAlpha preserveAspectRatio primitiveUnits
r radius refX refY renderingIntent repeatCount repeatDur requiredExtensions
requiredFeatures restart result rotate rx ry scale seed shapeRendering slope
spacing specularConstant specularExponent speed spreadMethod startOffset
stdDeviation stemh stemv stitchTiles stopColor stopOpacity
strikethroughPosition strikethroughThickness string stroke strokeDasharray
strokeDashoffset strokeLinecap strokeLinejoin strokeMiterlimit strokeOpacity
strokeWidth surfaceScale systemLanguage tableValues targetX targetY textAnchor
textDecoration textLength textRendering to transform u1 u2 underlinePosition
underlineThickness unicode unicodeBidi unicodeRange unitsPerEm vAlphabetic
vHanging vIdeographic vMathematical values vectorEffect version vertAdvY
vertOriginX vertOriginY viewBox viewTarget visibility widths wordSpacing
writingMode x x1 x2 xChannelSelector xHeight xlinkActuate xlinkArcrole
xlinkHref xlinkRole xlinkShow xlinkTitle xlinkType xmlns xmlnsXlink xmlBase
xmlLang xmlSpace y y1 y2 yChannelSelector z zoomAndPan

You may also use custom attributes as long as they’re fully lowercase.