I send an optional parameter checkbox inside a prop to a component:
var checkBox = this.props.checkbox ? <span className='checkbox'></span> : null;
Then I put it like this:
<div>
...
{checkBox}
...
</div>
As seen from above, I assign null to the variable. But I can instead assign empty string '' which seems to give the same result.
What's the proper one?
You need to use null. If you use an empty string like '' then react will create an empty span dom element, so it's not the same.
var label1 = <label>My Label</label>; // react generates a label element
var label2 = null; // react doesn't generate any dom element
var label3 = ''; // react generates and empty span like <span></span>
Use false, null or undefined.
This snippet shows the behaviour of rendering falsy values in React:
<meta charset="UTF-8">
<script src="https://fb.me/react-0.13.2.js"></script>
<script src="https://fb.me/JSXTransformer-0.13.2.js"></script>
<div id="app"></div>
<script type="text/jsx;harmony=true">void function() { "use strict";
var falsyValues = [false, 0, "" , null, undefined, NaN]
var App = React.createClass({
componentDidMount() {
[].slice.call(React.findDOMNode(this).childNodes)
.forEach(child => console.log(child.outerHTML))
},
render() {
return <div>
{falsyValues.map(falsy => <div id={'test-' + falsy}>
Before
{falsy}
After
</div>)}
</div>
}
})
React.render(<App/>, document.getElementById('app'))
}()</script>false, null and undefined don't generate anything:
<div id="test-false" data-reactid=".0.0"><span data-reactid=".0.0.0">Before</span><span data-reactid=".0.0.2">After</span></div>
<div id="test-null" data-reactid=".0.3"><span data-reactid=".0.3.0">Before</span><span data-reactid=".0.3.2">After</span></div>
<div id="test-undefined" data-reactid=".0.4"><span data-reactid=".0.4.0">Before</span><span data-reactid=".0.4.2">After</span></div>
Whereas '', 0 and NaN do:
<div id="test-0" data-reactid=".0.1"><span data-reactid=".0.1.0">Before</span><span data-reactid=".0.1.1">0</span><span data-reactid=".0.1.2">After</span></div>
<div id="test-" data-reactid=".0.2"><span data-reactid=".0.2.0">Before</span><span data-reactid=".0.2.1"></span><span data-reactid=".0.2.2">After</span></div>
<div id="test-NaN" data-reactid=".0.5"><span data-reactid=".0.5.0">Before</span><span data-reactid=".0.5.1">NaN</span><span data-reactid=".0.5.2">After</span></div>
As a convenience. you can conditionally generate content inline if the value you're testing against will be false, null or undefined when the conditional content shouldn't be displayed:
<div>
...
{this.props.checkbox && <span className='checkbox'></span>}
...
</div>