Foundations of Javascript - Types and Coercion

Types

• Variables don't have types, but the values don
  • You can have a variable 'X' that is assigned to a number type, but later you can assign a string to it.

NaN Value

• Global property value that represents not a number
• Used with Number.isNan(value) to check if a value is a number

new Keyword

• Used to instantiate a new object that has a constructor.

    var testDate = new Date();
    var smallCar = new Car("small");

Coercion & Type Conversion

• Coercion is implicit conversions of types.
• Type Conversion can be implicit or explicit.
• Implicit: "str" + 1, 1 is automatically converted to a string of "1"
• Explicit: Number("0x11") "0x11" is being told to become a number.

Booleans

• Falsy and Truthy, when converting values into booleans they become falsy and truthy.
• Falsy Values;
  • Empty String
  • undefined
  • null
  • 0, -0,
  • NaN
  • False
• Truthy Values;
  • Objects
  • Symbols
  • "populated string"
  • Numbers != 0 & -0
  • True
• Condition statements and loops will implicitly convert condition into a boolean but is better to explicit state them

    if(array.length){} //When length is 0 then condition is false, implicit.
    if(array.length > 0) {} //Explicit, when length is greater than 0 then true.

Equality

• == vs ===
  • ==, Checks if 2 operands value are equal.attempts to convert and compare operands of different types.
  • ===, Strict equality, checks values, but considers different operand types to be different
• ==, Allows coercion (Different types)
• ===, Doesn't allow coercion (Types need to be same)

    3 == '3' //True
    3 === '3' //False