Javascript string formatting, short question

Question

How can I use javascript to add a number (any number between 0-100) followed by a underscore, before the variable value?

Example:

 2000 becomes 12_2000 //a number of my choice is added followed by an underscore
 hello becomes 12_hello

The number (12 in this case) is a constant chosen by me!

Thanks

Answer 1

i + '_' + x where i is the number and x is an arbitrary value.

Answer 2

Just use string concatenation:

var res = '12_' + myNum;

Or with a variable prefix:

var res = prefix + '_' + myNum;

Answer 3

This is just basic string concatenation, which can be done with the + operator:

var num = 2000;
"12_" + num;
// "12_2000"

Answer 4

var_name = "2000";
output = "12_" + var_name;

Answer 5

function prefixWithNumber(value, number) {
 return number + "_" + value;
}

This expression is evaluated as (number + "_") + value. Since one of the operants in the first addition is a string literal, the second argument number is converted (coerced) to a string. The result is a string, which causes the third argument to be converted to a string as well.

This is what the JS engine does behind the scenes:

(number.toString() + "_") + value.toString();

Answer 6

Maybe you're looking for something like this:

Object.prototype.addPrefix = function(pre){
 return pre + '_' + this;
 };

This allows code like:

var a = 5;
alert(a.addPrefix(7));

or even:

"a string".addPrefix(7);

Answer 7

Joining an array can be faster in some cases and more interesting to program than "+"

[i, '_', myNum].join('')