Can a for loop increment/decrement by more than one?

问题

Are there other ways to increment a for loop in Javascript besides i++ and ++i? For example, I want to increment by 3 instead of one.

for (var i = 0; i < myVar.length; i+3) {
   //every three
}

回答1:

Use the += assignment operator:

for (var i = 0; i < myVar.length; i += 3) {

Technically, you can place any expression you'd like in the final expression of the for loop, but it is typically used to update the counter variable.

For more information about each step of the for loop, check out the MDN article.

回答2:

A for loop:

for(INIT; TEST; ADVANCE) {
    BODY
}

Means the following:

INIT;
while (true) {
    if (!TEST)
        break;
    BODY;
    ADVANCE;
}

You can write almost any expression for INIT, TEST, ADVANCE, and BODY.

Do note that the ++ operators and variants are operators with side-effects (one should try to avoid them if you are not using them like i+=1 and the like):

++i means i+=1; return i
i++ means oldI=i; i+=1; return oldI

Example:

> i=0
> [i++, i, ++i, i, i--, i, --i, i]
[0, 1, 2, 2, 2, 1, 0, 0]

回答3:

for (var i = 0; i < 10; i = i + 2) {
    // code here
}

回答4:

Andrew Whitaker's answer is true, but you can use any expression for any part.
Just remember the second (middle) expression should evaluate so it can be compared to a boolean true or false.

When I use a for loop, I think of it as

for (var i = 0; i < 10; ++i) {
    /* expression */
}

as being

var i = 0;
while( i < 10 ) {
    /* expression */
    ++i;
}

回答5:

You certainly can. Others have pointed out correctly that you need to do i += 3. You can't do what you have posted because all you are doing here is adding i + 3 but never assigning the result back to i. i++ is just a shorthand for i = i + 1, similarly i +=3 is a shorthand for i = i + 3.

回答6:

for (var i = 0; i < myVar.length; i+=3) {
   //every three
}

additional

Operator   Example    Same As
  ++       X ++        x = x + 1
  --       X --        x = x - 1
  +=       x += y      x = x + y
  -=       x -= y      x = x - y
  *=       x *= y      x = x * y
  /=       x /= y      x = x / y
  %=       x %= y      x = x % y

回答7:

The last part of the ternary operator allows you to specify the increment step size. For instance, i++ means increment by 1. i+=2 is same as i=i+2,... etc. Example:

let val= [];

for (let i = 0; i < 9; i+=2) {
  val = val + i+",";
}


console.log(val);

Expected results: "2,4,6,8"

'i' can be any floating point or whole number depending on the desired step size.

来源：https://stackoverflow.com/questions/12809776/can-a-for-loop-increment-decrement-by-more-than-one

标签

javascript

for-loop

increment