Writing in the front

Today is mourning wang, but can’t delay more. Fool also have to write na (no), when I write enough many, many, I will become a big bull.

The front is nonsense, today on the array! . API methods, hey, hey.

1, Every ()

The every() method tests whether all elements in an array pass the test of a given function. It returns a Boolean value.



const isBelowThreshold = (currentValue) => currentValue < 40;

const array1 = [1, 30, 39, 29, 10, 13];

console.log(array1.every(isBelowThreshold));
// expected output: true

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2. Filter ()

The filter() method creates a new array containing all the elements of the test implemented through the provided function.


const words = ['spray', 'limit', 'elite', 'exuberant', 'destruction', 'present'];

const result = words.filter(word => word.length > 6);

console.log(result);
// expected output: Array ["exuberant", "destruction", "present"]
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3, find ()

The find() method returns the value of the first element in the array that satisfies the provided test function. Otherwise return undefined.

const array1 = [5, 12, 8, 130, 44];
 
const found = array1.find(element => element > 10);
 
console.log(found);
// expected output: 12
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4, findIndex ()

The findIndex() method returns the index of the first element in the array that satisfies the provided test function. Returns -1 if no corresponding element is found.

const array1 = [5, 12, 8, 130, 44];
 
const isLargeNumber = (element) => element > 13;
 
console.log(array1.findIndex(isLargeNumber));
// expected output: 3
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5. Pop ()

The pop() method removes the last element from the array and returns the value of that element. This method changes the length of the array.

const plants = ['broccoli', 'cauliflower', 'cabbage', 'kale', 'tomato'];
 
console.log(plants.pop());
// expected output: "tomato"
 
console.log(plants);
// expected output: Array ["broccoli", "cauliflower", "cabbage", "kale"]
 
plants.pop();
 
console.log(plants);
// expected output: Array ["broccoli", "cauliflower", "cabbage"]
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6. Push ()

The push() method adds one or more elements to the end of an array and returns the array’s new length.

const animals = ['pigs', 'goats', 'sheep'];
 
const count = animals.push('cows');
console.log(count);
// expected output: 4
console.log(animals);
// expected output: Array ["pigs", "goats", "sheep", "cows"]
 
animals.push('chickens', 'cats', 'dogs');
console.log(animals);
// expected output: Array ["pigs", "goats", "sheep", "cows", "chickens", "cats", "dogs"]
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7, shift ()

The shift() method removes the first element from the array and returns the value of that element. This method changes the length of the array.

const array1 = [1, 2, 3];
 
const firstElement = array1.shift();
 
console.log(array1);
// expected output: Array [2, 3]
 
console.log(firstElement);
// expected output: 1
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8, unshift ()

The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array (this method modifies the original array).

const array1 = [1, 2, 3];
 
console.log(array1.unshift(4, 5));
// expected output: 5
 
console.log(array1);
// expected output: Array [4, 5, 1, 2, 3]
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9, join ()

The join() method joins all the elements of an array (or an array-like object) into a string and returns the string. If the array has only one item, that item is returned without a delimiter.

const elements = ['Fire', 'Air', 'Water'];
 
console.log(elements.join());
// expected output: "Fire,Air,Water"
 
console.log(elements.join(''));
// expected output: "FireAirWater"
 
console.log(elements.join('-'));
// expected output: "Fire-Air-Water"
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10, lastIndexOf ()

The lastIndexOf() method returns the index of the last element in the array specified (that is, a valid JavaScript value or variable), or -1 if none exists. Look forward from the back of the array, starting at fromIndex.

const animals = ['Dodo', 'Tiger', 'Penguin', 'Dodo'];
 
console.log(animals.lastIndexOf('Dodo'));
// expected output: 3
 
console.log(animals.lastIndexOf('Tiger'));
// expected output: 1
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11, Some ()

The some() method tests that at least one element in the array passes the provided function test. It returns a Boolean value.

const array = [1, 2, 3, 4, 5];
 
// checks whether an element is even
const even = (element) => element % 2 === 0;
 
console.log(array.some(even));
// expected output: true
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12. Slice ()

The slice() method returns a new array object that is a shallow copy (including begin, but not end) of the array determined by begin and end. The original array will not be changed.

const animals = ['ant', 'bison', 'camel', 'duck', 'elephant'];
 
console.log(animals.slice(2));
// expected output: Array ["camel", "duck", "elephant"]
 
console.log(animals.slice(2, 4));
// expected output: Array ["camel", "duck"]
 
console.log(animals.slice(1, 5));
// expected output: Array ["bison", "camel", "duck", "elephant"]
 
console.log(animals.slice(-2));
// expected output: Array ["duck", "elephant"]
 
console.log(animals.slice(2, -1));
// expected output: Array ["camel", "duck"]
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13, map ()

The map() method creates a new array with the result that each element in the array is the return value from a call to the provided function.

const array1 = [1, 4, 9, 16];
 
// pass a function to map
const map1 = array1.map(x => x * 2);
 
console.log(map1);
// expected output: Array [2, 8, 18, 32]
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14, reverse ()

The reverse() method reverses the position of the elements in the array and returns the array. The first element of the array becomes the last, and the last element of the array becomes the first. This method changes the original array.

const array1 = ['one', 'two', 'three'];
console.log('array1:', array1);
// expected output: "array1:" Array ["one", "two", "three"]
 
const reversed = array1.reverse();
console.log('reversed:', reversed);
// expected output: "reversed:" Array ["three", "two", "one"]
 
// Careful: reverse is destructive -- it changes the original array.
console.log('array1:', array1);
// expected output: "array1:" Array ["three", "two", "one"]
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15. ToString ()

ToString () returns a string representing the specified array and its elements.

const array1 = [1, 2, 'a', '1a']; console.log(array1.toString()); / / expected output: "1, 2, a, 1 a"Copy the code

Write in the last

Ah I finally C, ah no, finished writing, see you tomorrow friends, today is also hard-working Xiao Wang, cheers ~