当console.log（）时获得NaN

Question

I'm doing a project/game in HTML/JavaScript with a console, and I'm putting in "ping" in it. But when I run this code I just get "NaN".

function ping(IP){
    for (var i = 0; i <= 3; i++) {
        var start = new Date().getTime();
        console.log("64 bytes from " + IP + ": icmp_seq=" + i + " ttl=64 time: " + new Date().getTime() - start);
    };
}

Answer 1

The - is causing an implicit conversion of this string:

"64 bytes from " + IP + ": icmp_seq=" + i + " ttl=64 time: " + new Date().getTime()

to NaN . The + and - in your line are evaluated from left to right, so when you get to the - , you are evaluating String - Number . In JS, this causes the string to be converted to a number (or NaN if it cannot be converted), which is obviously not what you want. NaN - anything is still NaN .

By wrapping the (new Date().getTime() - start) in parentheses, the numerical operation is completed first, then you are adding together String + Number . This results in a conversion from number to string, so your console.log will work as you expect.

Answer 2

You can't directly use concatenation and math...

" ttl=64 time: " + new Date().getTime() - start);

So add the code in parenthesis as follows...

console.log("64 bytes from " + IP + ": icmp_seq=" + i + " ttl=64 time: " + (new Date().getTime() - start));

Answer 3

function ping(IP){
   for (var i = 0; i <= 3; i++) {
       var start = new Date().getTime();
       var newTime = new Date().getTime() - start;
       console.log("64 bytes from " + IP + ": icmp_seq=" + i + " ttl=64 time: " + newTime);
   };
}