Why cannot define array variable in state of react class?

Question

I've created a React class with state variable as array type.

export default class Demo extends React.Component {
  constructor(props){
    super(props)
    this.state ={
      test: []
    }
  }

Now, when I use console.log(this.state.test) in render function then it returns object type. I thought it is for the unique-key purpose when mapping.

But, what if I just want to define an array for push method?

Is there any other way to define the same? Please guide.

Have you tried pushing to it? It's definitely an array, but it's a key : value object. The objects property value is an array. test is not an array, it's just a key — Sterling Archer
– Sterling Archer, Commented Jul 8, 2017 at 1:43

gyre · Accepted Answer · 2017-07-08 11:25:34Z

2

Remember that array are objects in javascipt.

typeof([]) //outputs object

To print the array in readable form, you can use JSON.stringify

console.log(JSON.stringify(this.state.test, null, 2))

To set array in the state, you can use the setState method:

this.setState({test: [/* new array */]})

In react I really like to use the pre tag to show state while I'm developing.

Add this to render:

<pre>{JSON.stringify(this.state, null, 2)}</pre>

edited Jul 8, 2017 at 11:25

gyre

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answered Jul 8, 2017 at 2:04

Shayan C

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1 Comment

loganfsmyth Over a year ago

typeof is an operator, not a function, so the parens around [] are superfluous.

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