在打字稿中循环。 “ =预期”

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.

Answer 1

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);
}

Answer 2

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 .

Answer 3

// 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 .