如何在for循环中初始化数组？

Question

I want create a array like this.

itemList = ['1', '2', '3', '4', '5', '6', '7']

But my code's output is

itemList = ['1,2,3,4,5,6,7']

 var numberList = []; export default class App extends Component<{}> { constructor(props) { super(props); for (let i = 1; i < 8; i++){ numberList.push(i); } numberList = numberList.toString(); this.state = { selectedItem : 2, itemList: [numberList] }; } 

Answer 1

numberList = numberList.toString(); turns your whole array into a string. Then with itemList: [numberList] you create a new array that contains the string as one element.

To fix it:

• Use toString() on every value in the for loop instead on the actual array.
• Also remove the brackets from itemList: [numberList] . It should be itemList: numberList instead.

 var numberList = []; for (let i = 1; i < 8; i++){ numberList.push(i.toString()); } console.log(numberList); 

Answer 2

What happens in your code is that you construct the array:

[1,2,3,4,5,6,7]

And then call toString on it. Calling toString on an array will turn the entire array into a string, not turn each element of the array into the string. So you want to call the String constructor on each element as you iterate over 1 -> 8. The fixed code can be seen below.

Note: Not sure what the ultimate goal of this component is, but probably also want to change selectedItem in this.state from 2 -> '2', as I imagine it maps to the elements of itemList which are of type String now and not Number

 var numberList = []; export default class App extends Component<{}> { constructor(props) { super(props); for (let i = 1; i < 8; i++){ numberList.push(String(i)); } this.state = { selectedItem : 2, itemList: numberList }; } } 

Answer 3

// the following will convert the whole array as a string, avoid this // numberList = numberList.toString();

 var numberList = []; for (let i = 1; i < 8; i++){ numberList.push(i.toString()); } export default class App extends Component<{}> { constructor(props) { super(props); this.state = { selectedItem : 2, itemList: numberList }; } 

Answer 4

There is a way to do it without loop using spread on new Array and map that into values:

 /** * Creates an array from start to end where start is a number smaller than end * It takes an optional parameter called step that defaults to 1 * usage example: * range(5,9);// [5, 6, 7, 8, 9] * range(5,9,1.5);// [5, 6.5, 8] */ const range = (start,end,step=1)=>{ const min = start-step return [...new Array(Math.floor((end-min)/step))].map( (val,index)=>min+(step*(index+1)) ); }; console.log(range(5,9)); console.log(range(5,9,1.5));