Es2016 key summary

1.Array.prototype.includes

before：

Use Array.prototype.indexOf() To determine whether the array contains an element , Because this method returns the first index of a given element that can be found in the array , If it doesn't exist , Then return to -1.

const beasts = ['ant', 'bison', 'camel', 'duck', 'bison'];

console.log(beasts.indexOf('bison'));
// expected output: 1

// start from index 2
console.log(beasts.indexOf('bison', 2));
// expected output: 4

console.log(beasts.indexOf('giraffe'));
// expected output: -1

after：

Array.prototype.includes() Method is used to determine whether an array contains a specified value , According to the circumstances , Return if included true, Otherwise return to false.

const array1 = [1, 2, 3];

console.log(array1.includes(2));
// expected output: true

const pets = ['cat', 'dog', 'bat'];

console.log(pets.includes('cat'));
// expected output: true

console.log(pets.includes('at'));
// expected output: false

2. Index of operation

before：

Math.pow() Function returns cardinality （base） The index of （exponent） The next power , namely baseexponent.

console.log(Math.pow(7, 3));
// expected output: 343

console.log(Math.pow(4, 0.5));
// expected output: 2

console.log(Math.pow(7, -2));
// expected output: 0.02040816326530612
// (1/49)

console.log(Math.pow(-7, 0.5));
// expected output: NaN

after：

Use **

console.log(7 ** 3)
// expected output: 343

console.log(4 ** 0.5)
// expected output: 2

console.log(7 ** -2)
// expected output: 0.020408163265306124

console.log((-7) ** 0.5)
// expected output: NaN