Type Casting & Coercion

• Perform type coercion at the beginning of the statement.
• Strings:

// => this.reviewScore = 9;

// bad
const totalScore = this.reviewScore + '';

// good
const totalScore = String(this.reviewScore);

• Numbers: Use Number for type casting and parseInt always with a radix for parsing strings. eslint: radix

const inputValue = '4';

// bad
const val = new Number(inputValue);

// bad
const val = +inputValue;

// bad
const val = inputValue >> 0;

// bad
const val = parseInt(inputValue);

// good
const val = Number(inputValue);

// good
const val = parseInt(inputValue, 10);

• If for whatever reason you are doing something wild and parseInt is your bottleneck and need to use Bitshift for performance reasons, leave a comment explaining why and what you're doing.

// good
/**
  * parseInt was the reason my code was slow.
  * Bitshifting the String to coerce it to a
  * Number made it a lot faster.
  */
const val = inputValue >> 0;

• Note: Be careful when using bitshift operations. Numbers are represented as 64-bit values, but bitshift operations always return a 32-bit integer (source). Bitshift can lead to unexpected behavior for integer values larger than 32 bits. Discussion. Largest signed 32-bit Int is 2,147,483,647:

2147483647 >> 0 //=> 2147483647
2147483648 >> 0 //=> -2147483648
2147483649 >> 0 //=> -2147483647

• Booleans:

const age = 0;

// bad
const hasAge = new Boolean(age);

// good
const hasAge = Boolean(age);

// good
const hasAge = !!age;