奇怪的内部循环不执行某些迭代 [英] Weird inner loop not executing certain iterations

问题描述

我试图回答这个问题，在那里我遇到了奇怪的循环条件。
$ b $ pre $ code> for（index1 = 1; index1 <8; index1 ++）{
var op =' ＃';
for（index2 = index1; index2 - 1; index2--）{//这个循环对我来说很奇怪
op = op +'＃';
}
console.log（op）;

$ / code>

在检查每个外循环迭代的内循环有多少次迭代得到这个：
$ b

看，它记录 0,1,2,3,4,5,6 。

我的问题是：
$ b

内循环是不是在第一个外循环迭代迭代，因为 index2 - 1 等于零，这是假的？

解决方案

内部循环是不是迭代在第​​一个外部循环迭代，因为index2 - 1等于零，这是假的？

这是正确的。任何提供给条件的错误值立即停止循环。

Falsey值是 0 ， NaN ， null ， undefined ， 和 false 。

I was trying to answer this question where I encountered a weird loop condition.

for (index1 = 1; index1 < 8; index1++) {
  var op = '#';
  for (index2 = index1; index2 - 1; index2--) { //this loop is weird to me
    op = op + '#';
  }
  console.log(op);
}

Upon checking how many iterations the inner loop is making for each outer loop iteration I get this:

var x = 0;

for (index1 = 1; index1 < 8; index1++) {
  //var op = '#';
  for (index2 = index1; index2 - 1; index2--) {
    var log = {};
    log.a = x; //check value before increment
    x++;
    log.b = x; //check value after increment
    console.log(`outer: ${index1}, inner: ${index2}`, log);
  }
  console.log(x);
  x = 0;
  //console.log(op);
}

As you can see, it logs 0, 1, 2, 3, 4, 5, 6.

My questions is:

Is the inner loop not iterating on the first outer loop iteration because index2 - 1 is equal to zero, which is falsy?

解决方案

Is the inner loop not iterating on the first outer loop iteration because index2 - 1 is equal to zero, which is falsy?

That's correct. Any falsey value provided to the condition to the loop immediately halts the loop.

Falsey values are 0, NaN, null, undefined, "" and false.

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