What are the return data types of typeof in js? Summary of js typeof return type and type conversion

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js typeof has six return types:

undefined, string, boolean, number, symbol (ES6), Object, Function.

Note: There is no array array. If it is an array, object will be returned.

Forced type conversion of js
js provides two conversion functions: parseInt() and parseFloat(). The former converts the value to an integer, and the latter converts the value to a floating point number. Only by calling these methods on the String type can these two functions run correctly; for other types, NaN (Not a Number) is returned.
parseInt()

parseInt("1234blue");   //returns   1234
parseInt("0xA");   //returns   10
parseInt("22.5");   //returns   22
parseInt("blue");   //returns   NaN

parseInt() method also has base mode, which can convert binary, octal, hexadecimal or any other base Convert string to integer. The base is specified by the second parameter of the parseInt() method, as shown in the following example:

parseInt("AF",   16);   //returns   175
parseInt("10",   2);   //returns   2
parseInt("10",   8);   //returns   8
parseInt("10",   10);   //returns   10

If the decimal number contains leading 0s, it is best to use base 10 so that you do not accidentally get an octal value. For example:

parseInt("010");   //returns   8
parseInt("010",   8);   //returns   8
parseInt("010",   10);   //returns   10

parseFloat()
Another difference in using the parseFloat() method is that the string must represent a floating point number in decimal form, and parseFloat() has no base mode .

parseFloat("1234blue");   //returns   1234.0
parseFloat("0xA");   //returns   NaN
parseFloat("22.5");   //returns   22.5
parseFloat("22.34.5");   //returns   22.34
parseFloat("0908");   //returns   908
parseFloat("blue");   //returns   NaN

Boolean(value)——Convert the given value into Boolean type;

Boolean("");   //false   –   empty   string
Boolean("hi");   //true   –   non-empty   string
Boolean(100);   //true   –   non-zero   number
Boolean(null);   //false   -   null
Boolean(0);   //false   -   zero
Boolean(new   Object());   //true   –   object

Number(value)——Convert the given value to Convert a given value into a number (can be an integer or a floating point number);

Number(false)                  0
Number(true)                   1
Number(undefined)              NaN
Number(null)                   0
Number( "5.5 ")                5.5
Number( "56 ")                 56
Number( "5.6.7 ")              NaN
Number(new   Object())         NaN
Number(100)                    100

String(value)——Convert the given value into a string.

var   s1   =   String(null);   //"null"
var   oNull   =   null;
var   s2   =   oNull.toString();   //won't   work,   causes   an   error

Using js variable weak type conversion

<script>
var   str= &#39;012.345 &#39;;
var   x   =   str-0;
x   =   x*1;
</script>

The above example takes advantage of the weak type characteristics of js and only performs arithmetic operations to achieve string to number conversion. Type conversion, but this method is still not recommended.

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js typeof determines the data type of a variable

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