For loop in typescript. "= expected"

Question

I have been trying to write a simple for loop like below in typescript :

   j:any;
  x=[1,2,3,4,5,6,7];
  for(j in x){
     console.log(x[j]);
  }

I get so much errors even when i use this keyword 1.'=' expected.
2. Cannot find name 'j'.
3.Module parse failed: You may need an appropriate loader to handle this file type.

| this.x = [1, 2, 3, 4, 5, 6, 7]; | } |
PlanningComponent.prototype.for = function (let) { | if (let === void 0) { let = j in this.x; } | console.log(this.x[j]);

4.Duplicate identifier j
5.Unexpected token.

Please correct me where i went wrong.

I'm sort of wondering if you did any kind of reading or learning about TypeScript before starting to write your code. Declaring variables is very basic (actually in JavaScript as well as TypeScript). — user663031
– user663031, Commented Sep 3, 2017 at 17:49

porgo · Accepted Answer · 2017-09-03 15:53:32Z

2

You must add

const

for variables x and j:

const x = [1, 2, 3, 4, 5, 6, 7];
for (const j of x) {
  console.log(j);
}

answered Sep 3, 2017 at 15:53

porgo

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Comments

gsamaras · Accepted Answer · 2017-09-03 16:00:43Z

0

j will be an unused label in the first line of your code, discard it.

Then add the const keyword in both x and in the condition of the for loop, for `j, like this:

const x = [1, 2, 3, 4, 5, 6, 7];
for(const j in x) {
   console.log(x[j]);
}

Tip: for(var j in x) will work too. Read more in TypeScript for-in statement. Do not forget to use var though in that case, otherwise you will declare a global variable, named j.

edited Sep 3, 2017 at 16:00

answered Sep 3, 2017 at 15:54

gsamaras

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Comments

Hitmands · Accepted Answer · 2017-09-03 16:05:37Z

0

// you're assigning to a variable which was never declared
j:any;

// you're assigning to a variable which was never declared
x=[1,2,3,4,5,6,7];


for(j in x){
 console.log(x[j]);
}

/*** correct version should be ***/

let j: number = 0;
const x: number[] = [1, 2, 3, 4, 5, 6, 7];

for(; j < x.length; i++) {
  const num: number = x[j];
  console.log({index: j, value: num});
}

`for...in` shouldn't be used over arrays.

answered Sep 3, 2017 at 16:05

Hitmands

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`for...in` shouldn't be used over arrays.

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`for...in` shouldn't be used over arrays.