Conversion rules for JS data types

Rules for data type conversions

• 1 if there is only one value, judging whether this value is true or FALSE, follow only 0,nan, ' null,undefined these five are false and the rest are true
• 2 If two value comparisons are equal, follow these rules:
  • ![] ->false
  • []==[]->false
  • //val==val Two values may not be of the same data type, if two equals sign comparison, The default data type conversion
  • rule:
    • 1 Object = = object is never equal
    • 2 Object = = String
      • First convert the object to a string (method called ToString), Then compare
        • [] empty array to string is '
        • {} Convert to String "[Object,objec]"
    The
    • 3 Object = = Boolean type
      • object first converts the string (tostring method), then converts the string to a digit (number, "" The empty string is 0), the Boolean type is converted to a number (true is 1,false is 0), and finally two numbers Word comparison []==false->true
    • 4 Object = = Number
      • First convert the string to a string (toString) and then convert the string to Number, and then compare
    • 5 Number = = Boolean
      • convert Boolean to number
    • 6 Number = = String The
      • string is converted to a number
    • 7 String = = Boolean
      • all converted to numbers
    • 8 null==undefined result is true;
    • 9 null or undefined and any other data type comparisons are not equal
• 3 except = = is compared, = = = Comparison (absolute comparison)
  • val = = = Val2 Compares data types if the data types are different and certainly not equal

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Two values are compared, and if the data type is different, the default data type conversion

Object = = object: Compare the memory addresses of the respective representatives, the same address, and the different addresses are unequal

Object = = Number: First the object is ToString, then the result is the number, and the final comparison with the numbers

Object = = String: The object is first ToString and then compared

Object = = Boolean: All converted to digital

-String = = Number: string converted to Digital

-String = = Boolean: All converted to digital

Boolean = = Number: Boolean converted to Digital

->null = = undefined are equal, they are equal to themselves, besides and any other value do not want to wait

->nan = = NaN is not equal

Converts a value to a Boolean type: The!、!!、 boolean, if (num) condition means that you first convert num to Boolean to verify true or False

Only ', 0, NaN, null, undefined for false, the rest is true

! [] = = false: two = = The priority of the judgment is the lowest, it must be the right and left side of the expression, the results of the implementation of the comparison

! [] Convert to Boolean and then take back->false =>true

Conversion rules for JS data types