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Reactjs setState() with a dynamic key name?

Posted by: admin November 29, 2017 Leave a comment

Questions:

EDIT: this is a duplicate, see here

I can’t find any examples of using a dynamic key name when setting the state. This is what I want to do:

inputChangeHandler : function (event) {
    this.setState( { event.target.id  : event.target.value } );
},

where event.target.id is used as the state key to be updated. Is this not possible in React?

Answers:

Thanks to @Cory’s hint, i used this:

inputChangeHandler : function (event) {
    var stateObject = function() {
      returnObj = {};
      returnObj[this.target.id] = this.target.value;
         return returnObj;
    }.bind(event)();

    this.setState( stateObject );    
},

If using ES6 or the Babel transpiler to transform your JSX code, you can accomplish this with computed property names, too:

inputChangeHandler : function (event) {
    this.setState({ [event.target.id]: event.target.value });
    // alternatively using template strings for strings
    // this.setState({ [`key${event.target.id}`]: event.target.value });
}

Questions:
Answers:

How I accomplished this…

inputChangeHandler: function(event) {
  var key = event.target.id
  var val = event.target.value
  var obj  = {}
  obj[key] = val
  this.setState(obj)
},

Questions:
Answers:

When you need to handle multiple controlled input elements, you can add a name attribute to each element and let the handler function choose what to do based on the value of event.target.name.

For example:

inputChangeHandler(event) {
  this.setState({ [event.target.name]: event.target.value });
}

Questions:
Answers:

Can use a spread syntax, something like this:

inputChangeHandler : function (event) {
    this.setState( { 
        ...this.state,
        [event.target.id]: event.target.value
    } );
},

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