How can I determine the current line number in JavaScript?

问题

Does JavaScript have a mechanism for determining the line number of the currently executing statement (and if so, what is it)?

回答1:

var thisline = new Error().lineNumber

If that doesn't work in whatever environment you're using, you can try:

var stack = new Error().stack

Then hunt through the stack for the line number.

回答2:

you can use

function test(){
    console.trace();
}
test();

回答3:

A bit more portable between different browsers and browser versions (should work in Firefox, Chrome and IE10+):

function ln() {
  var e = new Error();
  if (!e.stack) try {
    // IE requires the Error to actually be throw or else the Error's 'stack'
    // property is undefined.
    throw e;
  } catch (e) {
    if (!e.stack) {
      return 0; // IE < 10, likely
    }
  }
  var stack = e.stack.toString().split(/\r\n|\n/);
  // We want our caller's frame. It's index into |stack| depends on the
  // browser and browser version, so we need to search for the second frame:
  var frameRE = /:(\d+):(?:\d+)[^\d]*$/;
  do {
    var frame = stack.shift();
  } while (!frameRE.exec(frame) && stack.length);
  return frameRE.exec(stack.shift())[1];
}

回答4:

You can try to parse a source of a function to seek some marks.
Here is a quick example (yes, it's messed a little).

function foo()  
{       
    alert(line(1));
    var a;
    var b;      
    alert(line(2));
}   
foo();

function line(mark)
{
    var token = 'line\\(' + mark + '\\)';       
    var m = line.caller.toString().match(
        new RegExp('(^(?!.*' + token + '))|(' + token + ')', 'gm')) || [];
    var i = 0;
    for (; i < m.length; i++) if (m[i]) break;
    return i + 1;
}

回答5:

you can try:

window.onerror = handleError;
function handleError(err, url, line){
   alert(err + '\n on page: ' + url + '\n on line: ' + line);
}

then throw an error where you want to know (not overly desired, but it might help you if you are debugging.

Note: window.onerror isn't defined/handled in WebKit or Opera (last time I checked)

回答6:

inject the following snippet to your code:

console.debug("line:", /\(file:[\w\d/.-]+:([\d]+)/.exec(new Error().stack)[1]);

回答7:

If your code is javascript + PHP, then the current PHP line number is available in javascript as a literal constant, because it's available in PHP as <?= __LINE__ ?>

(That's assuming you have PHP short tags enabled, obviously.)

So, for example, in javascript you can say:

this_php_line_number = <?= __LINE__ ?>;

However, if you are not careful, the PHP line number might be different from the javascript line number, because PHP "eats" source lines before the browser ever sees them. So the problem becomes ensuring that your PHP and javascript line numbers are the same. If they're different it makes using the browser's javascript debugger a lot less pleasant.

You can ensure the line numbers are the same by including a PHP statement that writes the correct number of newlines needed to synchronize server-side (PHP) and brower-side (javascript) line numbers.

Here's what my code looks like:

<!DOCTYPE html>
<html lang="en">
<!-- Copyright 2016, 2017, me and my web site -->
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="initial-scale=1, user-scalable=yes">

<?php

...lottsa PHP stuff here, including all PHP function definitions ...

echo str_repeat("\n",__LINE__-6); # synchronize PHP and Javascript line numbers
?>
<!-- *** this is line <?php echo __LINE__ . ' of ' . basename(__FILE__); ?> *** -->

  <title>My web page title</title>

...lottsa HTML & Javascript stuff here...

</body>
</html>
<!-- *** this is line <?php echo __LINE__ . ' of ' . basename(__FILE__); ?> *** -->

The key is this PHP statement:

echo str_repeat("\n",__LINE__-6);

That's spits out enough newlines to make the line number seen by javascript be the same as the PHP line number. All the PHP function definitions, etc. are at the top, ahead of that line.

After that line, I restrict my use of PHP to code that doesn't change the line numbers.

The "-6" accounts for the fact that my PHP code starts on line 8. If you start your PHP code earlier, you'll reduce that number. Some people put their PHP right at the very top, even ahead of the DOCTYPE.

(The meta viewport line disables Android Chrome "font boosting" per this stackoverflow Q&A: Chrome on android resizes font . Consider it boilerplate, which every web page needs.)

The following line is just for verifying that I haven't made a mistake. Viewed in the browser's debugger, or by right-click / save-web-page, it becomes an HTML comment which shows the correct source file name and line number:

<!-- *** this is line <?php echo __LINE__ . ' of ' . basename(__FILE__); ?> *** -->

becomes:

<!-- *** this is line 1234 of my_file.php *** -->

Now, wherever I see a line number, whether it's in an error message or in the javascript debugger, it's correct. PHP line numbers and javascript line numbers are always consistent and identical.

来源：https://stackoverflow.com/questions/2343343/how-can-i-determine-the-current-line-number-in-javascript

标签

javascript

line-numbers