How to analyze the usage of array types in classic js ability assessment questions_with code

I am currently working on a classic js ability assessment question, so I summarized it according to my own abilities and ideas. This article is mainly a summary of the array class.

1. Find the position of the element item in the given array: arr.indexOf(item);

2. Calculate the sum of all elements in the given array arr: arr .forEach(function(e){sum=sum e;})

Note: Array name.forEach(function(array element, element index, additionally defined array){function body}) / /What is returned is still the called array

Array name.map(function(array element){function body}) //What is returned is a new array, which does not modify the called array;

3. Remove the elements in the array arr whose ownership is equal to item. Do not modify the array arr directly. The result will be a new array.

function remove(arr, item) {
    var newArray=[];
    arr.forEach(function(e){
        if(e!=item){
            newArray.push(e);
        }
    })
    return newArray;
}

4. Remove all elements in the array arr that are equal to item, directly modify the given array, and return the result.

//方法一:从前往后遍历删除元素
function removeWithoutCopy(arr,item){
    for(i=0;i<arr.length;i++){
        if(item==arr[i]){
            arr.splice(i,1); //splice(定位元素索引[,删除元素个数,添加元素])
            i--;//i--的目的是因为删除了一个元素，在回到for时需要i++，会跳过一个元素
        }
    }
}

//方法二:从后往前遍历删除元素
function removeWithoutCopy(arr,item){
    for(i=arr.length-1;i>=0;i--){
        if(item==arr[i]){
            arr.splice(i,1); //删除时无需进行位移
        }
    }
}

Note: Array name.splice (index [, number, add elements]), splice means directly modifying the original array, and the return value is an array composed of deleted elements. Example: var a=[1,2,3,4,5];a.splice(3,1)//Return [4], a is [1,2,3,5]

5 , add the element item at the end of the array arr, do not modify arr directly, and return a new array.

//方法一:直接使用数组的concat追加新的item，并返回新的数组
function append(arr, item) {
    return arr.concat(item);
}

//方法二:利用slice对原数组进行切分，产生新的数组，在对新数组进行push即可
function append(arr, item) {
    var newArray=arr.slice(0);
    newArray.push(item);
    return newArray;
}
//方法三:利用数组的map创建新的数组，最后对新数组push(item)即可
function append(arr, item) {
    var newArray=arr.map(function(e){
        return e;
    })
    newArray.push(item);
    return newArray;
}
//方法四：定义一个空数组，利用for/forEach进行赋值，再对新数组push(item)即可
function append(arr, item) {
    var newArray=[];
    arr.forEach(function(e){
        newArray.push(e);
    })
    newArray.push(item);
    return newArray;
}

6. Delete the last element of array arr. Do not modify array arr directly. The result will be a new array: return arr.slice(0,arr.length-1);

7. Add element item at the beginning of array arr. Do not modify the array arr directly. The result will be a new array: var newArray=arr.slice(0);newArray.unshift(item)

8. Delete the first element of the array arr. Do not modify the array arr directly. The result is a new array: return arr.slice(1);

9. Merge array arr1 and array arr2. Do not modify the array arr directly. The result will be a new array: return arr1.concat(arr2);

10. Add the element item at the index of the array arr. Do not modify the array arr directly. The result is a new array: var newArray = arr.slice(0); newArray.splice(index,0,item); return newArray;

11. The median value of the statistical array arr is equal to The number of occurrences of item's elements.

function count(arr, item) {
    var count=0;
    arr.forEach(function(e){
        if(e==item)
            count+=1;
    });
    return count;
}

12. Find the repeated elements in the array arr. Input: [1, 2, 4, 4, 3, 3, 1, 5, 3]. Output: [1, 3, 4].

//方法一：利用indexOf和lastIndexOf进行判断
function duplicates(arr) {
    var result=[];
    arr.forEach(function(e){
        if(arr.indexOf(e)!=arr.lastIndexOf(e) && result.indexOf(e)==-1){
            result.push(e);
        }
    });
    return result;
}

//方法二：利用双重for循环进行判断
function duplicates(arr) {
    var result=[];
    for(i=0;i<arr.length-1;i++){
        for(k=0;k<result.length;k++){
            if(arr[i]==result[k])
                break;
        }
        if(k!=result.length) continue;
        for(j=i+1;j<arr.length;j++){
            if(arr[i]==arr[j]){
                result.push(arr[i]);
                break;
            }
        }
    }
    return result;
}

13. Find the second power of each element in the array arr. Do not modify the array arr directly, the result will be a new array.

//方法一：定义空数组，对arr进行遍历赋值
function square(arr) {
    var newArr=[];
    arr.forEach(function(e){
        newArr.push(e*e);
    });
    return newArr;
}
//方法二：直接使用map产生新的数组
function square(arr) {
    return arr.map(function(e){
        return e*e;
    })
}

14. In the array arr, find all positions where the element whose value is equal to item appears

function findAllOccurrences(arr, target) {
    var newArray=[];
    arr.forEach(function(e,i){
        if(e==target) newArray.push(i);
    })
    return newArray;
}

In the classic js questions, the above is the question type of all arrays, and then the following is It is a coding specification and function module.

Related recommendations:

BootStrap classic case analysis

PHP string operation classic introduction

Video tutorial: 27 classic practical exercises for front-end JS development

The above is the detailed content of How to analyze the usage of array types in classic js ability assessment questions_with code. For more information, please follow other related articles on the PHP Chinese website!