js five basic data types: string, number, boolean, null, undefined

/ * * 
 * Five basic data types: String, Number, Boolean, null, undefined 
 * / 
// undefined 
// declare variables foo, undeclared variable bar 
var foo; 
the console.log ( ` typeof foo: foo $ {}` , ` typeof bar: bar {} $`); // typeof foo: bar typeof undefined: undefined 
IF (foo === undefined) { // foo congruent undefined 
    the console.log ( 'foo congruent undefined' ); 
} the else { 
    the console.log ( 'foo insufficiency equal undefined' ); 
} 
IF ( typeof bar === 'undefined') { // bar congruent undefined
    console.log ( 'bar congruent undefined' ); 
} the else { 
    the console.log ( 'bar is not identical to undefined' ); 
} 
// typeof return string type 
the console.log ( ` typeof ( typeof foo): $ { typeof ( typeof foo)} `); // typeof (typeof foo): String 
// definition of function f (), but not the function thereof, the default is undefined 
function f () {} 
the console.log (` typeof f (): $ { typeof F ()} `,` F () === undefined: $ {F ()} `=== undefined); // typeof F (): F undefined () === undefined: to true 

// null
the console.log ( ` typeof Null: $ { typeof Null}`); // typeof Null: undefined 
the console.log ( ` typeof  null : $ { typeof  null }`); // typeof null: Object 

// String 
// Common escape character 
// --------------------------------------------- ------------------------------ 
// \ n-newline 
// \ T tab 
// \ space B 
// \ Enter r 
// \ F website page 
// \\ backslash 
// \ 'single quote 
// \ "double quotes
// \ 0nnn nnn octal representation of the character code (n is 0-7 in an octal number) 
// character \ xnn hex code nn represented (n is 0 to F in a hexadecimal number) 
// \ unnnn hexadecimal representation of the Unicode character code nnnn (n is 0 to F in a hexadecimal number) 
// ------------------- -------------------------------------------------- ------ 
var foo = 'Hello' ; 
the console.log ( ` typeof foo: $ { typeof foo}`); // typeof foo: String 

// Boolean 
var right = to true , 
    Wrong = to false ; 
the console.log ( ` typeof right: $ { typeof right},typeof wrong: ${typeof wrong}`); // typeof right: boolean, typeof wrong: boolean

// number
// 整型
var foo = 100;
console.log(`typeof foo: ${typeof foo}`); // typeof foo: number
// 八进制
var foo = 017;
console.log(foo); // 15
// 十六进制
var foo = 0xAB;
console.log(foo) // 171
// 浮点数
var foo = 23.01;
console.log(foo); // 23.01 
// maximum value of 
the console.log (Number.MAX_VALUE = $ { `` Number.MAX_VALUE}); // Number.MAX_VALUE 1.7976931348623157e + = 308 
// minimum 
console.log ( `Number.MIN_VALUE = $ { } `Number.MIN_VALUE); // Number.MIN_VALUE = 5E-324 
// positive infinity 
the console.log (as Number.POSITIVE_INFINITY = $ {` `as Number.POSITIVE_INFINITY}); // as Number.POSITIVE_INFINITY = infinity 
// negative infinity 
console .log (as Number.NEGATIVE_INFINITY = $ { `` as Number.NEGATIVE_INFINITY}); // as Number.NEGATIVE_INFINITY = -Infinity 
// isFinite limited number verification 
var foo = as Number.POSITIVE_INFINITY, 
    bar = foo. 3 * ;
 IF (isFinite (bar)) { // bar infinite numbers 
    console.log ( 'bar is a limited number' ); 
} the else { 
    the console.log ( 'bar infinite numbers' ); 
} 
// NaN3 not a number , specific values can not be used to directly calculate 
var foo = 'Hello' ;
 IF (isNaN (foo)) { // foo not a number 
    console.log ( 'foo not a number' ); 
} the else { 
    the console.log ( 'foo is digital ' ); 
}