Javascript concatination of strings?

You can force it to treat the operation as a string concatenation by starting the expression with a blank string, the "mode" of the operation will only change to string AFTER a string is encountered in the expression, but not before:

var x = 1;

var y = 2;

var concatString = "" + x + y;

// concatString == "12"

var concatString2 = x + y + "..." + x + y;

// concatString2 == "3...12"

Similarly, if you were concatenating strings but wanted to do a math operation within the string, it would need to be offset in parentheses:

var x = 1;

var y = 2;

var concatString = "The total weight is: " + x + y + "kg";

// concatString == "The total weight is: 12kg"

var sumString = "The total weight is: " + (x + y) + "kg";

// sumString == "The total weight is: 3kg"

A quick way to get something you've created as a string back to a number is to multiply it by 1 (a quick alternative to parseInt() if you know the string is only numbers).

var x = 1;

var y = 2;

var concatString = "" + x + y;

var badSum = concatString + 10;

// badSum == "1210"

var goodSum = concatString * 1 + 10;

// goodSum == 22

However, if your string could contain letters as well as numbers, this implicit "" + or the explicit String(x) cast will give you NaN (not a number). parseInt takes care of that:

var x = "1 apple";

var y = "2 apples";

var concatSum1 = x + y + " apples";

// concatSum1 == "1 apple2 apples apples"

var concatSum2 = Number(x) + Number(y) + " apples";

// concatSum2 == "NaN apples"

var concatSum3 = 1*x + 1*y + " apples";

// concatSum3 == "NaN apples"

var concatSum4 = parseInt(x) + parseInt(y) + " apples";

// concatSum4 == "3 apples"

I usually do it by adding the empty string first because if there is one known string value the the entire expression will be treated as a string.

var myString = "" + x + y;

However I believe you can also do it by casting like this.

var myString = String(x) + String(y)

Likewise you could force it to be a number

var myTotal = Number(x) + Number(y);

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