In React you can clearly create an object and assign it as an inline style. i.e.. mentioned below.
var divStyle = {
color: 'white',
backgroundImage: 'url(' + imgUrl + ')',
WebkitTransition: 'all', // note the capital 'W' here
msTransition: 'all' // 'ms' is the only lowercase vendor prefix
};
var divStyle2 = {fontSize: '18px'};
React.render(<div style={divStyle}>Hello World!</div>, mountNode);
How can I combine multiple objects and assign them together?
If you're using React Native, you can use the array notation:
<View style={[styles.base, styles.background]} />
Check out my detailed blog post about this.
You can do this with Object.assign().
In your example, you would do:
ReactDOM.render(
<div style={Object.assign(divStyle, divStyle2)}>
Hello World!
</div>,
mountNode
);
That will merge the two styles. The second style will replace the first if there are matching properties.
As Brandon noted, you should use Object.assign({}, divStyle, divStyle2) if you want to reuse divStyle without the fontSize applied to it.
I like to use this to make components with default properties. For example, here's a little stateless component with a default margin-right:
const DivWithDefaults = ({ style, children, ...otherProps }) =>
<div style={Object.assign({ marginRight: "1.5em" }, style)} {...otherProps}>
{children}
</div>;
So we can render something like this:
<DivWithDefaults>
Some text.
</DivWithDefaults>
<DivWithDefaults className="someClass" style={{ width: "50%" }}>
Some more text.
</DivWithDefaults>
<DivWithDefaults id="someID" style={{ marginRight: "10px", height: "20px" }}>
Even more text.
</DivWithDefaults>
Which will give us the result:
<div style="margin-right:1.5em;">Some text.</div>
<div style="margin-right:1.5em;width50%;" class="someClass">Some more text.</div>
<div style="margin-right:10px;height:20px;" id="someID">Even more text.</div>
Unlike React Native, we cannot pass array of styles in React, like
<View style={[style1, style2]} />
In React, we need to create the single object of styles before passing it to style property. Like:
const Header = (props) => {
let baseStyle = {
color: 'red',
}
let enhancedStyle = {
fontSize: '38px'
}
return(
<h1 style={{...baseStyle, ...enhancedStyle}}>{props.title}</h1>
);
}
We have used ES6 Spread operator to combine two styles. You can also use Object.assign() as well for the same purpose.
This also works if you don't need to store your style in a var
<Segment style={{...segmentStyle, ...{height:'100%'}}}>
Your content
</Segment>
Object.assign() is an easy solution, but the (currently) top answer's usage of it — while just fine for making stateless components, will cause problems for the OP's desired objective of merging two state objects.
With two arguments, Object.assign() will actually mutate the first object in-place, affecting future instantiations.
Ex:
Consider two possible style configs for a box:
var styles = {
box: {backgroundColor: 'yellow', height: '100px', width: '200px'},
boxA: {backgroundColor: 'blue'},
};
So we want all our boxes to have default 'box' styles, but want to overwrite some with a different color:
// this will be yellow
<div style={styles.box}></div>
// this will be blue
<div style={Object.assign(styles.box, styles.boxA)}></div>
// this SHOULD be yellow, but it's blue.
<div style={styles.box}></div>
Once Object.assign() executes, the 'styles.box' object is changed for good.
The solution is to pass an empty object to Object.assign(). In so doing, you're telling the method to produce a NEW object with the objects you pass it. Like so:
// this will be yellow
<div style={styles.box}></div>
// this will be blue
<div style={Object.assign({}, styles.box, styles.boxA)}></div>
// a beautiful yellow
<div style={styles.box}></div>
This notion of objects mutating in-place is critical for React, and proper use of Object.assign() is really helpful for using libraries like Redux.
Array notaion is the best way of combining styles in react native.
This shows how to combine 2 Style objects,
<Text style={[styles.base, styles.background]} >Test </Text>
this shows how to combine Style object and property,
<Text style={[styles.base, {color: 'red'}]} >Test </Text>
This will work on any react native application.
Actually, there is a formal way to combine and it is like below:
<View style={[style01, style02]} />
But, there is a small issue, if one of them is passed by the parent component and it was created by a combined formal way we have a big problem:
// The passing style02 from props: [parentStyle01, parentStyle02]
// Now:
<View style={[style01, [parentStyle01, parentStyle02]]} />
And this last line causes to have UI bug, surly, React Native cannot deal with a deep array inside an array. So I create my helper function:
import { StyleSheet } from 'react-native';
const styleJoiner = (...arg) => StyleSheet.flatten(arg);
By using my styleJoiner anywhere you can combine any type of style and combine styles. even undefined or other useless types don't cause to break the styling.
For ones that looking this solution in React, If you want to use the spread operator inside style, you should use: babel-plugin-transform-object-rest-spread.
Install it by npm module and configure your .babelrc as such:
{
"presets": ["env", "react"],
"plugins": ["transform-object-rest-spread"]
}
Then you can use like...
const sizing = { width: 200, height: 200 }
<div
className="dragon-avatar-image-background"
style={{ backgroundColor: blue, ...sizing }}
/>
More info: https://babeljs.io/docs/en/babel-plugin-transform-object-rest-spread/
So basically I'm looking at this in the wrong way. From what I see, this is not a React specific question, more of a JavaScript question in how do I combine two JavaScript objects together (without clobbering similarly named properties).
In this StackOverflow answer it explains it. How can I merge properties of two JavaScript objects dynamically?
In jQuery I can use the extend method.
To take this one even further, you could create a classnames-like helper function:
const styleRules = (...rules) => {
return rules.filter(Boolean).reduce((result, rule) => {
return { ...result, ...rule };
}, {});
};
And then use it conditionally in your components:
<div style={
styleRules(
divStyle,
(window.innerWidth >= 768) && divStyleMd,
(window.innerWidth < 768) && divStyleSm
)
}>Hello World!</div>
To Expand on what @PythonIsGreat said, I create a global function that will do it for me:
var css = function(){
var args = $.merge([true, {}], Array.prototype.splice.call(arguments, 0));
return $.extend.apply(null, args);
}
This deeply extends the objects into a new object and allows for a variable number of objects as parameters. This allows you to do something like this:
return(
<div style={css(styles.base, styles.first, styles.second,...)} ></div>
);
var styles = {
base:{
//whatever
},
first:{
//whatever
},
second:{
//whatever
}
}
