Why is this while loop looping infinitely? [closed]

问题

So i'm making a web app for my studies, it basically uses a combination of Twitter's streaming api and Google Maps to display the Lat Lng values.

Y is an element which states the number of tweets which have been received, ( checks length of an array) and X is another which has it's text content incremented by 1 every second.

I just put some random values for the time for it to take, I would use a more logical scale ( every 60 secs or something).

I wanted to log this information every minute, to make a graph but i've made an infinite loop somehow and i'm not quite sure how.

Here's the code:

function saveinfo(){
var x = document.getElementsByClassName('timer')[0].textContent;
var y = document.getElementsByClassName('counter')[0].textContent;
while (x != "510"){
    if(x = "5"){
        console.log(y);

    }
    else if (x = "200") {
        console.log(y);

    }
    else if (x = "300"){
        console.log(y);

    }
    else if (x = "400"){
        console.log(y);

    }
    else if (x = "500"){
        console.log(y);
        x = "510"
    }
}
};

回答1:

When your if statements are evaluated, you're setting x:

if(x = "5"){

This means that x will never equal "510", and your loop will go on forever.

To fix this, you should do something like if(x === '5')

回答2:

Three main reasons:

x is a local variable, not a reference to the content in the element. When the content changes, the value in x stays the same.
= is the assignment operator, not the comparison operator. You need to use == (or better, ===) for comparison. Since x = "5" evaluates to true, you will never get past the first if.
Your loop prevents the UI from updating anyway, because JavaScript is by default single-threaded. Even if you did read the value in the timer all the time rather than reading the local, it would still never change.

回答3:

Your if/else statements aren't working.
You put in if(x = "200") instead of if( x == "200").
In if/else statements, if(x=1)doesn't work.
if(x==1) or if(x=="1") always work.
if(x==="1") works only if x is a string that says "1".
if(x===1) only works if x is a number.

All you need to do is change the if(x="number") into if(x=="number")

来源：https://stackoverflow.com/questions/36460244/why-is-this-while-loop-looping-infinitely

标签

javascript

while-loop