Javascript Arithmetic Operator Subtract

Introduction

The subtract operator (-) is used as follows: 

let result = 2 - 1;

The subtract operator has special rules to deal with the variety of type conversions present in Javascript.

They are as follows:

  • If the two operands are numbers, perform arithmetic subtract and return the result.
  • If either operand is NaN, the result is NaN.
  • If Infinity is subtracted from Infinity, the result is NaN.
  • If -Infinity is subtracted from -Infinity, the result is NaN.
  • If -Infinity is subtracted from Infinity, the result is Infinity.
  • If Infinity is subtracted from -Infinity, the result is -Infinity.
  • If +0 is subtracted from +0, the result is +0.
  • If -0 is subtracted from +0, the result is -0.
  • If -0 is subtracted from -0, the result is +0.
  • If either operand is a string, a Boolean, null, or undefined, it is converted to a number using Number() and the arithmetic is calculated using the previous rules. If that conversion results in NaN, then the result of the subtraction is NaN.
  • If either operand is an object, its valueOf() method is called to retrieve a numeric value to represent it. If that value is NaN, then the result of the subtraction is NaN.
  • If the object doesn't have valueOf() defined, then toString() is called and the resulting string is converted into a number.

The following are some examples of these behaviors: 

let result1 = 5 - true;  // 4 because true is converted to 1 
let result2 = NaN - 1;   // NaN 
let result3 = 5 - 3;     // 2 

let result4 = 5 - "";    // 5 because "" is converted to 0 
let result5 = 5 - "2";   // 3 because "2" is converted to 2 
let result6 = 5 - null;  // 5 because null is converted to 0



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