每个开发人员都应该掌握的 JavaScript 数组方法（第 1 部分）

const cuties = [
  { name: "wanda maximoff", age: 31 },
  { name: "natasha romanoff", age: 32 },
  { name: "jane foster", age: 27 },
  { name: "gwen stacy", age: 26 },
];

// find method returns the value of the first element 
// in the array that satisfies the given function 
// or else returns undefined
let cuty = cuties.find(({ age }) => age >= 30);

// output: { name: 'wanda maximoff', age: 31 }
console.log(cuty);

const cuties = [
  { name: "wanda maximoff", age: 31 },
  { name: "natasha romanoff", age: 32 },
  { name: "jane foster", age: 27 },
  { name: "gwen stacy", age: 26 },
];

// findindex method returns the index of the first array element 
// that satisfies the provided test function or else returns -1.
let cutyindex = cuties.findindex(({ age }) => age >= 30);

// output: 0
console.log(cutyindex);

const productprices = [5, 12, 3, 20, 5, 2, 50];

// indexof() returns the first index of occurance 
// of an array element, or -1 if it is not found.
let firstindex = productprices.indexof(20);
console.log(firstindex); // 3

let secondindex = productprices.indexof(5);
console.log(secondindex); // 0

// the second argument specifies the search start index
let thirdindex = productprices.indexof(5, 1);
console.log(thirdindex); // 4

// indexof returns -1 if not found
let notfoundindex = productprices.indexof(15);
console.log(notfoundindex); // -1

const avengers = ["captain", "tony", "thor", 
                  "natasha", "bruce", "clint"];

// modifies the array in place
avengers.sort(); 

// [ 'bruce', 'captain', 'clint', 'natasha', 'thor', 'tony' ]
console.log(avengers);  

const nums = [1000, 50, 2, 7, 14];

// number is converted to string and sorted
nums.sort(); 

// output: [ 1000, 14, 2, 50, 7 ]
console.log(nums) 

// sort nums in ascending order by providing compare function
nums.sort((a, b) => a - b);

// output: [ 2, 7, 14, 50, 1000 ]
console.log(nums);

const avengers = ["captain", "tony", "thor", 
                 "natasha", "bruce", "clint"];

// includes() method returns true if an array contains 
// a specified element or else returns false.
let check1 = avengers.includes("thor");
console.log(check1); // true 

// second argument specifies position to start the search
let check2 = avengers.includes("thor", 3);
console.log(check2); // false

// the search starts from the 4th-to-last element ("hulk") 
// and checks the rest of the array for "thor". 
let check3 = avengers.includes("thor", -4);
console.log(check3); // true

const nums = [120, 150, 80, , 200];

// foreach() method executes a provided 
// function for each array element which 
// have values. it returns undefined.

/*
num 0: 120
num 1: 150
num 2: 80
num 4: 200
*/
nums.foreach((value, index) => {
    console.log('num ' + index + ': ' + value);
});

const fruits = ["apple", "banana", "orange", "grape", "mango"];

// slicing the array (from start to end)
let slicedfruits1 = fruits.slice();
console.log(slicedfruits1); // [ 'apple', 'banana', 'orange', 'grape', 'mango' ]

// slicing from the third element
let slicedfruits2 = fruits.slice(2);
console.log(slicedfruits2); // [ 'orange', 'grape', 'mango' ]

// slicing from the second element to fourth element
let slicedfruits3 = fruits.slice(1, 4);
console.log(slicedfruits3); // [ 'banana', 'orange', 'grape' ]

// slicing the array from start to second-to-last
let slicedfruits4 = fruits.slice(0, -1);
console.log(slicedfruits4); // [ 'apple', 'banana', 'orange', 'grape' ]

// slicing the array from third-to-last
let slicedfruits5 = fruits.slice(-3);
console.log(slicedfruits5); // [ 'orange', 'grape', 'mango' ]

let animals = ["dog", "cat", "elephant", "lion"];

// replacing "elephant" & "lion" with "tiger" & "giraffe"
let removedanimals1 = animals.splice(2, 2, "tiger", "giraffe");
console.log(removedanimals1); // [ 'elephant', 'lion' ]
console.log(animals); // [ 'dog', 'cat', 'tiger', 'giraffe' ]

// adding elements without deleting existing elements
let removedanimals2 = animals.splice(1, 0, "elephant", "lion");
console.log(removedanimals2); // []
console.log(animals); // [ 'dog', 'elephant', 'lion', 'cat', 'tiger', 'giraffe' ]

// removing 3 elements
let removedanimals3 = animals.splice(2, 3);
console.log(removedanimals3); // [ 'lion', 'cat', 'tiger' ]
console.log(animals); // [ 'dog', 'elephant', 'giraffe' ]

const nums1 = [ 1 , 2 , 3 , 4 , 5];

// every() method returns true if all the array 
// elements pass the given test function or else
// returns false
let result1 = nums1.every(element => element < 6);

// output: true
console.log(result1); 

const nums2 = [ 1 , 2 , 7 , 4 , 5];
let result2 = nums2.every(element => element < 6);

// output: false
console.log(result2);

const nums1 = [ 8 , 2 , 7 , 9 , 6];

// some() method returns true if any of the array 
// elements pass the given test function or else 
// returns false
let result1 = nums1.some(element => element < 6);

// Output: true
console.log(result1); 

const nums2 = [ 8 , 6 , 7 , 9 , 10];
let result2 = nums2.some(element => element < 6);

// Output: false
console.log(result2);