React component initialize state from props
You don't need to call setState
in a Component's constructor
- it's idiomatic to set this.state
directly:
class FirstComponent extends React.Component {
constructor(props) {
super(props);
this.state = {
x: props.initialX
};
}
// ...
}
See React docs - Adding Local State to a Class.
There is no advantage to the first method you describe. It will result in a second update immediately before mounting the component for the first time.
It should be noted that it is an anti-pattern to copy properties that never change to the state (just access .props directly in that case). If you have a state variable that will change eventually but starts with a value from .props, you don't even need a constructor call - these local variables are initialized after a call to the parent's constructor:
class FirstComponent extends React.Component {
state = {
x: this.props.initialX,
// You can even call functions and class methods:
y: this.someMethod(this.props.initialY),
};
}
This is a shorthand equivalent to the answer from @joews below. It seems to only work on more recent versions of es6 transpilers, I have had issues with it on some webpack setups. If this doesn't work for you, you can try adding the babel plugin babel-plugin-transform-class-properties
, or you can use the non-shorthand version by @joews below.