JS method to find the largest element in a Number type array

This article mainly introduces how to use JS to find the maximum element in a Number type array

How to use JS to find the maximum (or minimum) number in a Number type array?

Four methods are introduced below.

1. Do not use any library functions

The code is as follows:

function findMax1 (arr) { let result = 0; if (Array.isArray(arr)) { for (let i = 0; i < arr.length; i++) { result = arr[i] > result ? arr[i] : result; } return result; } else { console.error('The parameter arr is not an array'); return; } }

Explanation:

Use a variable result to store the maximum value. Traverse the array to be searched. If the currently traversed element is greater than result, assign this element to result.

2. Using Array.reduce()

The code is as follows:

function findMax2 (arr) { let result = 0; if (Array.isArray(arr)) { result = arr.reduce((a, b) => { return a > b ? a : b; }, 0); return result; } else { console.error('The parameter arr is not an array'); return; } }

Explanation:

The reduce method uses a function to finally reduce an array to a value for an accumulator and each element in the array.

reduce accepts two parameters:

The first one is callback, which is the function mentioned earlier. It has four parameters:

1. accumulator: Accumulator, which is the result of the last callback run. If initialValue is provided, then the first time is initialValue;

2. currentValue: the elements of the currently traversed array;

3. currentIndex: the currently traversed The index of the array element, starting from 0. If initialValue is provided, it starts from 1;

4. array: the array to which reduce is currently applied.
   

The second is initialValue, which is an initial value and is used as the first actual parameter of the first run of the callback function. This is optional. Please note here that if this parameter is not provided and is applied to an empty array, an error will be reported.

Then the meaning of the above code is that every time the array is traversed for comparison, the larger one is left, that is, the accumulator, and used for the next comparison with the array elements. In the end, only this value is left, which is the maximum value.

3. Using Apply and Math.max()

The code is as follows:

function findMax3 (arr) { let result = 0; if (Array.isArray(arr)) { result = Math.max.apply(null, arr); return result; } else { console.error('The parameter arr is not an array'); return; } }

Explanation:

applyThe explanation is slightly complicated and no further explanation will be given.

It accepts two parameters, the first is thisArg and the second is argsArray. Both are optional. To put it simply, when using a function, the parameters are passed in as an array.

4. Only use Math.max()

The code is as follows:

function findMax4 (arr) { let result = 0; if (Array.isArray(arr)) { result = Math.max(...arr); return result; } else { console.error('The parameter arr is not an array'); return; } }

Explanation :

Based on the idea of the previous solution, in ES6, there is a spread operator (...) that can separate the elements in an array into a sequence separated by commas. Just meets the needs of the Math.max() function.

Let me introduce to you some knowledge points related to number, Math and arrays in JS

1. Number object.

How to create a Number object:

Method 1:

var variable = new Number (number)

Method 2:

var variable = number;

Commonly used method:

toString() Convert the number into the specified base form String. (Enter a number and it will be converted to number, number.toString(2))

toFixed() specifies that decimal places are retained and it also has a rounding function.

2. Math

Commonly used methods of Math objects:

ceil Round up

floor() Round down

random() random number method // The pseudo-random number generated is between 0 and 1 (including 0, excluding 1),

round rounding

3. Array array object:

Method 1 to create an array:

var variable name = new Array(); Create an array with a length of 0.

Method 2:

var variable name = new Array(length) creates an array object of specified length.

Method 3:

var variable name = new Array("Element 1", "Element 2"...); Create an array object by specifying elements in the array.

Method 4:

var variable name = ["Element 1", "Element 2"...];

Details to note for arrays:

1. The length of an array can change in javascript.

var arr = new Array(); //创建了一个长度为0的数组对象。 arr[100] = 10; document.write("arr长度："+arr.length+"
"); var arr2 = new Array("狗娃","狗剩","铁蛋"); arr2 = ["狗娃","狗剩","铁蛋","张三"]; document.write("arr2长度："+arr2.length+"
");

3.1 Number method

a、concat把arr1与arr2的数组元素组成一个新的数组返回。　　 arr1 = arr1.concat(arr2);

b, join uses the specified separator Concatenate the elements in the array into a string and return it.

var elements = arr1.join(",");

c, pop: Remove the last element in the array and return that element.

d, push: Add new elements to an array and return the new length value of the array.

arr1.push("你好");

e, reverse(); Flip the elements of the array

f, slice specifies the start index value and end index value of the array to intercept the array elements, and returns the subarray. (The header is not included, the tail is not included)

var subArr = arr1.slice(1,2);

g, sort sorting, the sorting method must be passed in when sorting. (When not passed, the default is to arrange according to the ASCII table)

arr1 = [19,1,20,5]; arr1.sort(sortNumber); //排序，排序的时候一定要传入排序的方法。 function sortNumber(num1,num2){ return num1-num2; }

h, the first parameter of splice is the index value to start deleting elements, and the second parameter is the deletion The number of elements, the subsequent data is the inserted elements (you don’t need to write it).

arr1.splice(1,1,"张三","李四","王五");

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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