increment in for loop javascript

It prints 1, 1, 1, 1, 1 because you reset numberin every iteration.

change your code to:

for (var i = 0; i < 5; i++) {
    console.log(i);
}

or

var number = 0;
for (var i = 0; i < 5; i++) {
    console.log(number);
    number++;
}

(Answer to additional question in comments) You get 1,2,3,4,5 because you increment number before you print it.

You keep resetting the value of number to 0. Try setting it before the loop:

var number= 0
for (var i = 0; i < 5; i++) {
    console.log(number);
    number++
}

you can do this

<script>
var number = 0;
for (var i = 0; i < 5; i++) {
    number++;
    console.log(number);
    alert(number)
}
</script>

The issue with your code is that you're declaring the number variable inside the for loop, so it gets reinitialized to 0 with each iteration. To fix this, you should declare the number variable outside the loop, before it starts. Here's the corrected code:

for (var i = 0; i < 5; i++) {
  number++;
  console.log(number);

With this change, the number variable will retain its value across iterations, and you'll see the expected output of 0, 1, 2, 3, 4 in the console.

If you just want to iterate in range from 0 to 5, you can use "i" variable.

for (let i=0; i<5; i++) {
   console.log(i);
}

but if you need use for some reason another variable as you name it "number", in javascript you can write too as belowe

let number = 0;
for (let i=0; i<5; i++) {
   console.log(number++);
}

or

for (let i=0, number=0; i<5; i++) {
   console.log(number++);
}