What are the types of JavaScript variables and the conversion methods between variables

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1. Variable type var num = 10; console.log (typeof num)

Typeof: declare variable types

Alert: pop-up alert box

Prompt: input and output statements

1.1 Color of variable type

Identify variable types according to the color of the console:

Purple: numerical type

Black: character type

Blue: Boolean (true false)

Light gray: undefined null

two。 Literal quantity

A literal is a representation of a fixed value in the source code, that is, a literal representation of how the value is expressed.

3. Data type conversion 3.1. Convert to string type 1. Plus sign concatenation string

Console.log (num+' I am the string')

2.toString () converted to string var num=10;var str=num.toString (); console.log (str); 3.string (variable) 3.2 converted to numeric (key) 1.parseInt (string) function-"integer numeric var age=prompt ('Please enter your age'); console.log (parseInt (age)); console.log (parseInt ('3.14')) / / rounding 3 console.log (parseInt ('3.98')); / / rounding 3 console.log (parseInt (' 120px')); / / rounding 1202.parseFloat (string) function-- "floating-point numeric console.log (parseFloat ('3.14'); console.log (parseFloat (' 120px')); / / 120 removes the px unit 3. Using number (variable) var str='123';console.log (number (str); console.log (number ('123')); 4. Take advantage of arithmetic operations-+ * / implicit conversion console.log ('123mur0); / 12console.log (' 123humor 120'); / 3console.log ('123conversation 1); / 1233.3 convert to Boolean type

Boolean () function

Return value: true or false

False: 0, NaN, null, undefined,''(empty)

Console.log (boolean (')); / / falseconsole.log (boolean (0)); / / falseconsole.log (boolean (NaN)); / / falseconsole.log (boolean (null)); / / falseconsole.log (boolean (undefined)); / / false

The rest are true.

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