A Please write the value of the following expression
var A =. 5; var B = 0;
(. 1) "" + A - B; _____5_______
(2) typeof ( "" + A - B); ___number________
(. 3) Boolean ( A) - B; _____1______
var n-= null; var m;
(. 4) typeof (n-); ____object_____
(. 5) typeof (m); ____undefined_____
(. 6) Number The (n-) + Number The (m); _____NaN_______
(. 7) Boolean (n-) - Boolean ( "n-"); _____- 1_______
(. 8) Boolean (m) - Boolean (n-); _____0________
(. 9) M--; ____NaN_______
(10) n-+; _____0______
two fill in the blank
(1) array method elements may be added, but does not modify the original array is ____concat______, the method can add elements to the array is arbitrary position ____splice______
(2) only __ ____ capable of letters, underline _____ __, __ _____ $ variable name as the beginning of
the three elements of the array (3): __ _____ subscript, ___ ____ element, the array length ______ __
0 was RES4 = (AGE1 - AGE2) || AGE1 + AGE2; 20
var C = 12 is ;
var RES1 = "" && C; 12 is
var RES2 = "NaN3" && C; 12 is
var RES3 = undefined || C + "C"; 12c
console.log ( Number ( "123.1.1abc" ) ); NaN
console.log ( parseInt ( "123.1.1abc" ) ); 123
console.log ( parseFloat ( "123.1.1abc" ) ); 123.1
console.log ( Number ( false ) ); 0
console.log ( Number ( undefined ) ); NaN
console.log(+null); 0
console.log(+"false"); NaN
console.log(+false); 0
console.log(+undefined); NaN
console.log(+"number"); NaN
var a = 5;
var b = 0;
console.log ( a+b ); 5
console.log ( typeof (a+b) ); number
console.log ( a-b ); 5
console.log ( typeof (a-b) ); number
console.log ( a-Boolean(b) ); 5
console.log ( typeof (a-Boolean(b)) ); number
console.log ( Boolean(a)-b ); 1
console.log ( typeof (Boolean(a)-b) ); number
console.log ( Boolean ( 0 ) ); flase
console.log ( Boolean ( 0.0 ) ); flase
console.log ( Boolean ( "0" ) ); true
console.log ( Boolean ( null ) ); flase
console.log ( Boolean ( "null" ) ); true
console.log ( Boolean ( false ) ); flase
console.log ( Boolean ( undefined ) ); flase
console.log ( Boolean ( ' ' ) ); true
console.log ( Boolean ( NaN ) ); flase
console.log ( Boolean ( "false" ) ); true
console.log ( Boolean ( "undefined" ) ); true
转成数字类型
parseInt(".123abc"); NaN
parseFloat(".12.3abc"); 0.12
parseInt(123); 123
parseFloat(123); 123
parseInt(123.25); 123
parseFloat(123.25); 123.25
console.log ( Number ( "123" ) ); 123
console.log ( Number ( "123.1.1abc" ) ); NaN
console.log ( parseInt ( "123.1.1abc" ) ); 123
console.log ( parseFloat ( "123.1.1abc" ) ); 123.1
console.log ( Number ( false ) ); 0
console.log ( Number ( undefined ) ); NaN
console.log(+null); 0
console.log(+"false"); NaN
console.log(+false); 0
console.log(+undefined); NaN
console.log(+"number"); NaN
var a = 5;
var b = 0;
console.log ( a+b ); 5
console.log ( typeof (a+b) ); number
console.log ( a-b ); 5
console.log ( typeof (a-b) ); number
console.log ( a-Boolean(b) ); 5
console.log ( typeof (a-Boolean(b)) ); number
console.log ( Boolean(a)-b ); 1
console.log ( typeof (Boolean(a)-b) ); number
console.log ( Boolean ( 0 ) ); flase
console.log ( Boolean ( 0.0 ) ); flase
console.log ( Boolean ( "0" ) ); true
console.log ( Boolean ( null ) ); flase
console.log ( Boolean ( "null" ) ); true
console.log ( Boolean ( false ) ); flase
console.log ( Boolean ( undefined ) ); flase
console.log ( Boolean ( ' ' ) ); true
console.log ( Boolean ( NaN ) ); flase
console.log ( Boolean ( "false" ) ); true
console.log ( Boolean ( "undefined" ) ); true
console.log ( Number ( "123" ) ); 123
console.log ( Number ( "123.1.1abc" ) ); NaN
console.log ( parseInt ( "123.1.1abc" ) ); 123
console.log ( parseFloat ( "123.1.1abc" ) ); 123.1
console.log ( Number ( false ) ); 0
console.log ( Number ( undefined ) ); NaN
console.log(+null); 0
console.log(+"false"); NaN
console.log(+false); 0
console.log(+undefined); NaN
console.log(+"number"); NaN
var a = 5;
var b = 0;
console.log ( a+b ); 5
console.log ( typeof (a+b) ); number
console.log ( a-b ); 5
console.log ( typeof (a-b) ); number
console.log ( a-Boolean(b) ); 5
console.log ( typeof (a-Boolean(b)) ); number
console.log ( Boolean(a)-b ); 1
console.log ( typeof (Boolean(a)-b) ); number
console.log ( Boolean ( 0 ) ); flase
console.log ( Boolean ( 0.0 ) ); flase
console.log ( Boolean ( "0" ) ); true
console.log ( Boolean ( null ) ); flase
console.log ( Boolean ( "null" ) ); true
console.log ( Boolean ( false ) ); flase
console.log ( Boolean ( undefined ) ); flase
console.log ( Boolean ( ' ' ) ); true
console.log ( Boolean ( NaN ) ); flase
console.log ( Boolean ( "false" ) ); true
console.log ( Boolean ( "undefined" ) ); true
隐式数据类型转换
console.log ( 1 + "true" ); 1true
console.log ( 1 + undefined ); NaN
console.log ( 1 + null ); 1
console.log ( 1 + false ); 1
console.log ( 1 + NaN ); NaN
console.log ( 1 + "null" ); 1null
console.log ( 1 + "10" ); 110
console.log ( "1" + 10 ); 110
console.log ( "1" + (10 + 1) ); 111
console.log ( "1" + 10 + 1 );`` 1101
console.log ( 10 + 1 + "1" ); 111
console.log ( !10 ); flase
console.log ( !"10" ); flase
console.log ( !"0" ); flase
console.log ( !0 ); true
console.log ( !"null" ); flase
console.log ( !"" ); true
console.log ( !" " ); flase