Firebug通过使用或+组合字符串来显示控制台中的字体更改

Question

I have come across an interesting effect on firebug, when using the + operator or the , operator to concatonate strings and then print something to the console the font changes based on which operator you used.

In this case the font for the word Harry changes:

Why does this happen? Isn't the comma operator used for concatonation as well?

Answer 1

No the comma is not used for concatenation. console.log will independently log each of its arguments to the same line on the console but if you separate arguments with commas, they will not be concatenated. The + operator will concatenate them. For example:

console.log('hello', {foo: 'bar'}); //=> 'hello', {foo: 'bar'}

console.log('hello' + {foo: 'bar'}); //=> 'hello[object Object]'

Using the + operator, JavaScript will attempt to call .toString on the object in order to concatenate it onto the previous string. Using the comma, each piece is considered its own argument passed to console.log which then logs each one.

As far as why firebug changes the font, I couldn't say. What I can say is that it has nothing to do with the actual JavaScript in your application.