Some common JavaScript API, full text hand buckle, inevitable error, welcome to point out!

1. String

1. charAt()

Returns the character of the specified index.

Parameters:

index

var str = "You can't go home without buying your ticket in advance.";

console.log(str.charAt(0));  / / call
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2. charCodeAt()

Returns the Unicode encoding of the character specified index.

Parameters:

index

console.log(str.charCodeAt(1)); / / 20320
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3. concat()

String concatenation.

Parameters:

The string to concatenate

console.log(str.concat("!!!")); // If you don't buy a ticket in advance, you can't go back!!
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4. String.fromCharCode()

Returns the character corresponding to the specified Unicode encoding.

Parameters:

Unicode

console.log(String.fromCharCode(1996)); / / ߌ
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5. indexOf()

Retrieves one string from another, returning the index of the first occurrence of the string, -1 if not found

Parameters:

The string to retrieve

console.log(str.indexOf("Buy")); / / 5
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6. lastIndexOf()

Retrieves one string from another, returning the index of the last occurrence of the string, -1 if not found

Parameters:

The string to retrieve

console.log(str.lastIndexOf("No")); / / 9
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7. match()

Finding one or more matches returns an array of matches. The contents of the array depend on whether regexp has the global flag G.

Parameters:

Matching rules (regular expressions or strings)

var str2 = "Jquery 3.6.0";

console.log(str2.match("J")); // ['J', index: 0, input: 'Jquery 3.6.0', groups: undefined]

console.log(str2.match(/\d/g)); // ['3', '6', '0']

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8. replace()

The first argument to replace the matched string can also be a normal string

Parameters:

Matching rules (regular expressions or strings)
The new string to be replaced by (or the return value of a callback function)

console.log(str.replace("You"."我")); // I can't go back without buying my ticket in advance
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9. search()

Retrieves the string matching the regular expression, returns index, -1 if not found

Parameters:

Matching rules (regular expressions or strings)

console.log(str.search(/ I forgot /)); // -1
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10. slice()

Intercepts a string in the specified range (left closed and right open) and returns the intercepted new string.

Parameters:

The starting index
End index (not available)

console.log(str.slice(0.3)); / / call you don't
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11. split()

Splits a string into arrays, returning arrays.

Parameters:

A reference to partition

console.log(str.split("")); / / [' call ', 'you', 'no', 'ask', 'before' and 'buy' and 'ticket', ', ', 'back', 'no', 'to', 'a', ' ']
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12. substring()

Intercepts a string in the specified range (left closed and right open) and returns the intercepted new string. The parameter cannot be negative

Parameters:

The starting index
End index (not available)

console.log(str.substring(0.2)); / / call you
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13. substr()

Intercepts a string of the specified length. Returns the intercepted new string.

Parameters:

The starting index
The number of characters to intercept

console.log(str.substr(1.2)); / / you don't
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14. toUpperCase()

Converts letters in a string to uppercase.

console.log(str2.toUpperCase()); / / JQUERY 3.6.0
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15. toLowerCase()

Converts letters in a string to lowercase.

console.log(str2.toLowerCase()); / / jquery 3.6.0
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16. length

Returns the length of the string, which is an attribute rather than a method.

console.log(str2.length); / / 12
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Second, the array

1. length

Returns the length of the array, which is a property, not a method.

var arr = [1.2.3.4.5.6.7.8];

console.log(arr.length); / / 8
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2. concat()

Concatenation of arrays. Returns the new array after concatenation, without changing the original array.

Parameters:

The array to concatenate

console.log(arr.concat([9.10])); // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
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3. push()

Adds one or more elements to the end of an array. Returns the new length of the array after the addition of elements, changing the original array.

Parameters:

The element to be added

console.log(arr.push(88)); / / 9
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4. pop()

Removing the last element at the end of the array, returning the deleted element, changes the array.

console.log(arr.pop()); / / 88
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5. unshift()

Adding one or more elements to the beginning of an array returns the new length of the array, changing the array.

Parameters:

The element to be added

console.log(arr.unshift(0)); / / 9
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6. shift()

Removes the first element at the beginning of the array, returning the deleted element. It changes the original array.

console.log(arr.shift()); / / 0
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7. reverse()

Reverses the order of the elements in an array. It changes the original array.

console.log(arr.reverse()); // [8, 7, 6, 5, 4, 3, 2, 1]
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8. join()

Concatenate the elements of an array into a string, returning a string without changing the array.

Parameters:

Concatenation symbol

console.log(arr.join()); / / 8,7,6,5,4,3,2,1
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9. slice()

Intercepts elements in the specified range (left closed and right open) to form a new array, without changing the original array.

Parameters:

The starting index
End index (not available)

console.log(arr.slice(0.2)); // [8, 7]
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10. splice()

Removes any element from any position in the array and inserts a new element at that position. It changes the original array. Returns an array of deleted elements.

Parameters:

The starting index
Number of elements to delete (if this parameter is 0, it becomes insert element here)
The element to be inserted at this position

console.log(arr.splice(0.1.999)); / / [8]
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11. indexOf()

Retrieves the first occurrence of an element in the array and returns its index, -1 if not found

Parameters:

The element to find

console.log(arr.indexOf(3)); / / 6
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12. lastIndexOf()

Retrieves the last occurrence of an element in the array and returns its index, -1 if not found

Parameters:

The element to find

console.log(arr.lastIndexOf(3)); / / 6
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13. sort()

Sorts arrays by the specified rule, by default, in ascending order by the element’s Unicode encoding. It changes the original array.

Parameters:

Callback function (return value >0, two adjacent elements swap positions, otherwise not)

console.log(arr.sort()); // [1, 2, 3, 4, 5, 6, 666, 7, 999]
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Three, date,

1. getFullyear()

Return now is that year.

console.log(mydate.getFullYear()); / / 2021
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2. getMonth()

Returns the current month, counting from 0.

console.log(mydate.getMonth()); / / 4
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3. getDate()

Returns the current day of the month.

console.log(mydate.getDate()); / / 5
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4. getDay()

Return to what day of the week it is.

console.log(mydate.getDay()); / / 3
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5. getHours()

Returns the current hour.

console.log(mydate.getHours()); / / 17
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6. getMinutes()

Returns the current number of minutes.

console.log(mydate.getMinutes()); / / 1
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7. getSeconds()

Returns the current number of seconds.

console.log(mydate.getSeconds()); / / 45
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8. getMilliseconds()

Returns the current number of milliseconds.

console.log(mydate.getMilliseconds()); / / 916
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9. getTime()

Returns the current timestamp.

console.log(mydate.getTime());  / / 1620205407916
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Four, Numbers,

1. toFixed()

Preserves the decimal of the specified number of digits.

Parameters:

Keep the number of decimal places

var num = -256.1024;

console.log(num.toFixed(2)); // -256.10
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2. parseInt()

Integer.

Parameters:

The number to round.
Base (indicates that the parameter 1 is calculated as a base number, which will be converted to base 10 and rounded)

console.log(parseInt(num)); / / - 256
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3. Number.isInteger()

Checks if it is an integer and returns a Boolean value.

Parameters:

The number to judge.

console.log(Number.isInteger(num));  // false
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4. Number.isNaN()

Returns a Boolean value to determine if it is not a number.

Parameters:

The number to judge.

console.log(Number.isNaN(num)); // false
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5. Number. MAX_VALUE and Number. MIN_VAUE

Both are attributes that represent the maximum and minimum number in JavaScript.

console.log(Number.MAX_VALUE, Number.MIN_VALUE); / / 1.7976931348623157 e+308 5 e - 324
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5. Mathematical methods

1. Math.PI

π in mathematics. This is a property.

console.log(Math.PI); / / 3.141592653589793
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2. Math.abs()

Take the absolute value.

console.log(Math.abs(-5.6)); / / 5.6
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3. Math.ceil()

Round up.

console.log(Math.ceil(3.1)); / / 4
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4. Math.floor()

I’m going to round down.

console.log(Math.floor(3.9));  / / 3
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5. Math.round()

Round off.

console.log(Math.round(3.5));  / / 4
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6. Math.random()

Select a random number between 0 and 1, with left on and right on.

console.log(Math.random());  / / 0.06899281638748667
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7. Math.pow()

Take some power of some number.

Parameters:

digital
How many times the power

console.log(Math.pow(2.10));  / / 1024
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8. Math.sqrt()

The square root operation, or the open root.

Parameters:

The number that I took the square root of

console.log(Math.sqrt(9)); / / 3
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Sixth, other

1. The encodeURIComponent () and decodeURIComponent ()

EncodeURIComponent: Encodes the string as a URI component.

DecodeURIComponent: Decodes the URI encoded by encodeURIComponent().

var url = "http://www.google.com";

var str = encodeURIComponent(url); 

console.log(str); // http%3A%2F%2Fwww.google.com

console.log(decodeURIComponent(str)); // http://www.google.com
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【 continuously update 】Js common methods

1. String

1. charAt()

2. charCodeAt()

3. concat()

4. String.fromCharCode()

5. indexOf()

6. lastIndexOf()

7. match()

8. replace()

9. search()

10. slice()

11. split()

12. substring()

13. substr()

14. toUpperCase()

15. toLowerCase()

16. length

Second, the array

1. length

2. concat()

3. push()

4. pop()

5. unshift()

6. shift()

7. reverse()

8. join()

9. slice()

10. splice()

11. indexOf()

12. lastIndexOf()

13. sort()

Three, date,

1. getFullyear()

2. getMonth()

3. getDate()

4. getDay()

5. getHours()

6. getMinutes()

7. getSeconds()

8. getMilliseconds()

9. getTime()

Four, Numbers,

1. toFixed()

2. parseInt()

3. Number.isInteger()

4. Number.isNaN()

5. Number. MAX_VALUE and Number. MIN_VAUE

5. Mathematical methods

1. Math.PI

2. Math.abs()

3. Math.ceil()

4. Math.floor()

5. Math.round()

6. Math.random()

7. Math.pow()

8. Math.sqrt()

Sixth, other

1. The encodeURIComponent () and decodeURIComponent ()

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