对于(;;)循环说明

Question

在JS中,我偶然发现了一种for循环,for(;;)就像while(true)循环一样.分号在for循环的括号中起什么作用？

Answer 1

for (statement 1; statement 2; statement 3) {
    code block to be executed
}

语句1是可选的,在循环(代码块)开始之前执行.

var i = 0;
var length = 10
for (; i < length; i++) { 

    //The for loop run until i is less than length and you incerement i by 1 each time. javascript doesnt care what you do inside, it just check whether you have variable with name i and length
}

语句2再次是可选的,定义了运行循环的条件(代码块).

var i = 0;
var len = 100;
for (i = 5; ; i++) { 
    //Here you are just initializing i with 5 and increment it by 1 there is no break condition so this will lead to an infinite loop hence we should always have a break here somehwere.
}

语句3是可选的,每次执行循环(代码块)后执行.

var i = 0;
var length = 100;
for (; i < length; ) { 
    //Here you are just checking for i < length which is true. If you don't increment i or have an break it will turn into infinite loop
}

在没有条件或初始化的情况下,在坚果壳中,它变成无限循环.