Blue number in Chrome Dev Console?

Question

In javascript I have a variable that I push to console.log then increment it and push it to the log again, which shows the below in the Chrome Dev Tools.

Answer 1

When you print a string using console.log you get black output. However, if you print a number the output is blue. See the screenshot bellow (don't mind the lines with 'undefined' value as this is what console.log() returns by default).

And you are right, your problems with += are somehow connected to these colours. You were adding number to a string which resulted in concatenation (53).

Answer 2

Note the difference between using commas and plus signs in console.log()

console.log( 'console.log("(" + 1 + ")"); // string concat' );
console.log("( " + 999 + " )"); 

console.log( 'console.log("(", 1, ")"); // string, number (blue), string' );
console.log("(", 999, ")");