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Javascript Addition( + ) & Subtraction( - )

The addition operator (+) adds numbers.

var a = 9,
 b = 3,
 c = a + b;


c will now be 12

This operand can also be used multiple times in a single assignment:

var a = 9,
 b = 3,
 c = 8,
 d = a + b + c;


d will now be 20.

Both operands are converted to primitive types. Then, if either one is a string, they're both converted to strings and
concatenated. Otherwise, they're both converted to numbers and added.

null + null; // 0
null + undefined; // NaN
null + {}; // "null[object Object]"
null + ''; // "null"

If the operands are a string and a number, the number is converted to a string and then they're concatenated,
which may lead to unexpected results when working with strings that look numeric.

"123" + 1; 


"1231" (not 124)

If a boolean value is given in place of any of the number values, the boolean value is converted to a number (0 for
false, 1 for true) before the sum is calculated:

true + 1; // 2
false + 5; // 5
null + 1; // 1
undefined + 1; // NaN

If a boolean value is given alongside a string value, the boolean value is converted to a string instead:

true + "1"; // "true1"
false + "bar"; // "falsebar"

Subtraction (-)

The subtraction operator (-) subtracts numbers.

var a = 9;
var b = 3;
var c = a - b;


c will now be 6

If a string or boolean is provided in place of a number value, it gets converted to a number before the difference is calculated (0 for false, 1 for true):

"5" - 1; // 4
7 - "3"; // 4
"5" - true; // 4

If the string value cannot be converted into a Number, the result will be NaN:

"foo" - 1; // NaN
100 - "bar"; // NaN


In this page (written and validated by ) you learned about Javascript Addition and Subtraction . What's Next? If you are interested in completing Javascript tutorial, your next topic will be learning about: Javascript Multiplication and Division.

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