JS Reading Summary

1. Number:
Nan is a result of an operation that does not produce normal results. The function isNaN (number) can be used to detect Nan;
The Math.floor method can convert a number to an integer;
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2. These listed values are treated as false (false): false, null, undefined, empty string "", number 0, and number nan;
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3, ternary operator:
Format: (conditional expression)? Expression 1: expression 2;//: int a = 10; int b = (a==b)? 10:20; Result is 20
If the expression arithmetic value is true, Ze produces the value of the second operand, and if false, produces the value of the third operand.
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4. Search:
var stu = {"first_name": "Jack"}
Stu.first_name or stu["first_name"]//Running results jack
|| The operator can be used to populate the default values:
var stu_mid = stu["Mid_name"] | | "(none)";
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5. Reduce the pollution of global variables: (Create only one unique global variable for the application and make this variable a container):
var vessel = {};
Vessel.one = "text";//The value of text can be obtained by vessel.one in the whole JS
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6. Apply Call Mode: (the Apply method has two parameters, one is the value to bind to this, and one is the parameter array)
var add = function (A, b) {
return a + B;
};
var array = [3, 4];
var sum = add.apply (null, array); The value of//sum is 7;
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7. Method:
1) Array:
Array.concat (item): Concat method produces a new array, similar to Array.push (item)
var a = [' A ', ' B ', ' C '];
var b = [' X ', ' y ', ' Z ']
var C = A.concat (b, true);//c becomes [' A ', ' B ', ' C ', ' X ', ' y ', ' z ', True]
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Array.join (separator): Separator default, separated, if you want to splice the empty string ""
var a = [' A ', ' B ', ' C '];
A.push (' d ');
var c = a.join (")//c for ' ABCD '
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Array.pop (): Removes the last element in the array and returns the element--its corresponding method Array.shift (): Removes the first element and returns the element
var a = [' A ', ' B ', ' C '];
var c = A.pop ();//a is [' A ', ' B '] & C is ' C '
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Array.push (Item ...): Appends one or more parameters to the end of an array--array.unshift (item:) Attaches one or more parameters to the head of an array
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Array.reverse (): Flips the order of elements in an array
var a = [' A ', ' B ', ' C '];
var B = A.reverse ();//a and B are [' C ', ' B ', ' a ']
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Array.slice (Start, end): Copy from start to end, default end to array length
var a = [' A ', ' B ', ' C '];
var b = A.slice (0, 1);//b is [' a ']
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Array.Sort (COMPAREFN): Sorts the contents of an array, but only for strings, and if you want to sort on a number, the following methods are available:
var n = [4,8,15,16,23,42];
N.sort (function (b) {
return a-B;
});//n is [4,8,15,16,23,42]
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Array.splice (Start, DeleteCount, item): Removes one or more elements and replaces them with item
var a = [' A ', ' B ', ' C '];
var r = A.splice (1, 1, ' ache ', ' bug ');
A is [' a ', ' ache ', ' Bug ', ' C '] r is [' B ']
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2) String:
String.charat (Index): Returns the character code point of the character at the index position in the string--string.charcodeat (index) that is returned by this position
var name = ' Curly ';
var end = Name.charat (0);//end is C
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String.Concat (string.): equivalent to the string + up, less use, because with + convenient
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String.match (RegExp): This method matches a string to a regular expression, depending on the G representation to determine how to match
var a =/regular expression/g;
var b = ' aaaaa ';
var i = B.match (a);
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String.Replace (Searchvalue, Replacevalue): Finding and replacing
Searchvalue if it is a regular expression with a G-id, ze replaces all matching
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String.slice (Start, end): Copy from start to end, default end to array length
var text = ' and in it ';
var a = Text.slice (0, 3);//a is ' and '
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String.Split (separator, limit): Splits a string to create an array of characters, and limit is an optional parameter that shows the number of split fragments
var text = ' 0123456789 ';
var a = Text.split (', 5);//a is [' 0 ', ' 1 ', ' 2 ', ' 3 ', ' 4 ']
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String.substring (Start,end): Similar to slice, except that this cannot handle negative integer parameters
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String.tolowercase (): Convert all to lowercase format;
String.touppercase (): Convert all to uppercase format;
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String.fromCharCode (char.): Returns a string based on numeric encoding
var a = String.fromCharCode (67,97,116);//a is ' Cat '
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8. typeof Operator:
typeof 98;//return number
typeof "98";//returns string
typeof null;//returns object instead of NULL
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9, parseint () most commonly used, can filter out non-numeric characters, such as 123blue will be converted to 123;
parseint ("08");//will get 0
parseint ("08", 10);//The result is 8. It is therefore recommended to add this count parameter.
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10, try to use = = = and! = =, avoid using = = and! =
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JS Reading Summary