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One, the extension of the stringHello everyone, here is "learn the Web series from scratch" and synchronize updates at the following address ...
- Github:https://github.com/daotin/web
- Public number: The top of the Web front
- Blog Park: http://www.cnblogs.com/lvonve/
- csdn:https://blog.csdn.net/lvonve/
Here I will start with the Web front End 0 Foundation, step-up learning web-related knowledge points, during the period will also share some fun projects. Now let's go to the Web Front end learning Adventure tour!
includes(str): Determines whether the specified string is included
startsWith(str): Determines whether to start with the specified string
endsWith(str): Determines whether to end with the specified stringrepeat(count): Repeat specified number of times
Second, the expansion of the valuelet str = 'abcdefg'; console.log(str.includes('a')); //true console.log(str.includes('h')); //false //startsWith(str) : 判断是否以指定字符串开头 console.log(str.startsWith('ab')); //true console.log(str.startsWith('ac')); //false //endsWith(str) : 判断是否以指定字符串结尾 console.log(str.endsWith('fg')); //true console.log(str.endsWith('d')); //false //repeat(count) : 重复指定次数a console.log(str.repeat(3)); // abcdefgabcdefgabcdefg
Binary and octal numeric representations: binary with 0b the beginning, octal with the 0o beginning.
Number.isFinite(i): To determine whether a finite number is a large
Number.isNaN(i): Determine if it is Nan
Number.isInteger(i): Determines whether an integer
Number.parseInt(str): Converts a string to the corresponding numeric valueMath.trunc(i): Direct removal of decimal parts
Console.log (0b1010);//10 Console.log (0o56);//46 console.log ('--------------------'); Number.isfinite (i): Determine whether a finite number of Console.log (Number.isfinite (NaN)); False Console.log (Number.isfinite (5)); True Console.log (Number.isfinite (Infinity)); False Console.log ('--------------------'); Number.isnan (i): Determine if it is a Nan Console.log (Number.isnan (Nan)); True Console.log (Number.isnan (5)); False Console.log (Number.isnan (undefined)); False Console.log ('--------------------'); Number.isinteger (i): Determine whether it is an integer console.log (Number.isinteger (5.23)); False Console.log (Number.isinteger (5.0)); True Console.log (Number.isinteger (5)); True Console.log ('--------------------'); Number.parseint (str): Converts a string to the corresponding numeric Console.log (Number.parseint (' 123abc ')); 123 Console.log (Number.parseint (' a123abc ')); NaN console.log ('--------------------'); Math.trunc (i): direct removal of the minor part Console.log (Math.trunc (13.123)); Array.from(v): Converts a pseudo-array object or a traversed object to a true arrayArray.of(v1, v2, v3): Converts a series of values to an array
find(function(value, index, arr){return true}): Find the first element that satisfies a condition that returns truefindIndex(function(value, index, arr){return true}): Finds the first element subscript that satisfies a condition that returns true
<body> <button> test 1</button> <br> <button> test 2</button> <br> <bu tton> Test 3</button> <br> <!--1. Array.from (v): Converts a pseudo-array object or a traversed object to a true array of 2. Array.of (v1, V2, v3): Converts a series of values to an array of 3. Find (function (value, index, arr) {return true}): Finds the first element that satisfies a condition that returns true 4. FindIndex (function (value, index, arr) {return true}): Find the first element that satisfies the condition returns true subscript--<script type= "Text/javascript" >//array.from (v): Converts a pseudo-array object or a traversal object to a true array, the return value is a true array//the collection of elements obtained using DOM manipulation is a pseudo-array. Let Btns = document.getelementsbytagname (' button '); Console.log (btns.length); 3 Array.from (Btns). ForEach (function (item, index) {console.log (item, index); }); Array.of (v1, V2, v3): Converts a series of individual values to an array of let arr = array.of (1, ' abc ', TRUE); Console.log (arr); Find (function (value, index, arr) {return true}): Find the first element that satisfies the condition return true Let arr1 = [1, 3, 5, 2, 6, 7, 3]; Let result = Arr1.find (function (itEM, index) {//Find the first element in the ARR1 array that is greater than 3 return item > 3; }); Console.log (result); 5//findindex (function (value, index, arr) {return true}): Find the first element that satisfies the condition returns true subscript let Result1 = Arr1.findinde X (function (item, index) {//finds the first element in the ARR1 array that is greater than 3 subscript value return item > 3; }); Console.log (RESULT1); 2 </script></body>Object.is(v1, v2): Determines whether 2 data is exactly equal. (internal is the implementation principle is to compare whether strings are exactly equal)console.log(Object.is('abc', 'abc'));//trueconsole.log(NaN == NaN);//falseconsole.log(Object.is(NaN, NaN));//trueconsole.log(0 == -0);//trueconsole.log(Object.is(0, -0));//false
Object.assign(target, source1, source2..): Copy the properties of the source object onto the target objectlet obj = {name : 'Daotin', age : 18, c: {d: 2}};let obj1 = {};Object.assign(obj1, obj);console.log(obj1, obj1.name);
__proto__ PropertiesV. Set container and Map containerlet obj3 = {name : 'Daotin', age : 18};let obj4 = {};// obj4的隐式原型指向obj3obj4.__proto__ = obj3;console.log(obj4, obj4.name, obj4.age);// {name : 'Daotin', age : 18} Daotin 18
Set Container : An unordered collection of multiple value that cannot be duplicated.
The set container needs to create a set container object through new, and the parameter is multiple value values.
let set = new Set([1,2,3,4,3,2,1,6]);
The methods and properties of the Set container object:
Set(): Constructor for Set container (without parameter value collection)Set(array): Constructor for set container (with parameter value collection)add(value): Adds a value to the Set container objectdelete(value): Delete value value of Set container objecthas(value): Determines whether the set container has value valuesclear(): Emptying the Set containersize: equivalent to the length of the arraymap Container : An unordered key does not repeat multiple key-value of the collection body.
Note: The collection of map parameter arrays, each array is in the form of Key-value. The entire array of the outside of the collection is
[]surrounded by, instead of{}.
let map = new Map([['name', 'Daorin'],['age', 18]]);
Map (Array)
Size
The role of set and map:
1. Set container can be heavy for an array.
let arr = [1, 2, 3, 4, 5, 2, 4, 5]; let set = new Set(arr); arr = []; for (let i of set) { arr.push(i); } console.log(arr); // 1,2,3,4,5
2, set and map containers can be used for ..of.. to traverse.
1. Exponential operator:**
console.log(3**2); // 9
2 Array.prototype.includes(value); : Determines whether the array contains the specified value. (In ES6, str.includes(str1) : Determine if str contains the specified string str1)
let arr = [1,2,3,4, 'abc'];console.log(arr.includes(2));//trueconsole.log(arr.includes('a'));//false
Learn the ES6 of the Web from scratch (vi) ES6 Basic Grammar Four
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