带有负数的 Javascript for 循环

Question

谁能告诉我为什么这些 javascript 循环不运行？

for(var i = -5; i == 0; i++) {
    document.write(i);
}

https://jsfiddle.net/0h2p6uod/

for(var i = -5; i == -1; i++) {
    document.write(i);
}

https://jsfiddle.net/xb4k0sub/

for(var i = -5; i == 5; i++) {
    document.write(i);
}

https://jsfiddle.net/4bbatja9/

然而，所有这些循环都在运行:

for(var i = -5; i < 0; i++) {
    document.write(i);
}

for(var i = -5; i < -1; i++) {
    document.write(i);
}

for(var i = -5; i < 5; i++) {
    document.write(i);
}

Answer 1

条件部分正在测试 true。如果 false，则循环停止。

for :

condition

An expression to be evaluated before each loop iteration. If this expression evaluates to true, statement is executed. This conditional test is optional. If omitted, the condition always evaluates to true. If the expression evaluates to false, execution skips to the first expression following the for construct.

for(var i = -5; i == 0; i++) {
//              ^^^^^^  false -> no loop