1.in:
For array properties, you need to specify the index value in the form of a number to represent the property name of the array
var arr = ["a","b","2","3","str"];
var result = ("b" in arr);
var result1 = (4 in arr);
console.log(result+'\n');
console.log(result1);
The output is:
speak
ture
For general object properties, you need to specify the name of the property as a string
Such as:
var goods={name:'instant noodles',count:1,year:1998}
if('name' in goods) // true
if('count' in goode)// true
2: indexOf() usage
You can determine whether a string appears in an array;
Such as:
var year=[1993,1994,1995,1996]
if(year.indexOf(1993)==-1)//return flase. If 1993 is not in the year array, return true.
if(year.ondexOf(2001)==-1)//return true. If 2001 is in the year array, return flase.
This method will retrieve the string from beginning to end to see if it contains a substring, and if so, return the position of the first occurrence of the substring
Such as:
var string = 'hello word'
console.log(string.indexOf('e')+'\n');
console.log(string.indexOf('w')+'\n');
console.log(string.indexOf('W'));
result:
1
6
-1
3.js ternary operator
The syntax is conditional ? result 1: result 2 ; . Here you write the condition in front of a question mark (?) followed by result 1 and result 2 separated by a colon (:). The result is 1 if the condition is met, otherwise the result is 2.
Such as
var a=1;
(a==1) ? a='true':b='flase';
console.log(a)
result: true
4: The role of the double vertical bar in the return value of the js function
|| means or,
var a=b||c;
It means that if b has a value, a=b, if b has no value, a=c. If there is no value, it is undefined .