This time I will show you how to use JS to find the maximum element of a Number type array, and what are the precautions for using JS to find the maximum element of a Number type array. The following is a practical case, let's take a look.
Four methods are introduced below.1. Do not use any library function
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; } }
2. Use 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; } }
3. Use 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; } }
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; } }
Math objectCommonly used methods:
ceil round upfloor() round down random() random number method // The pseudo-random number generated is between 0 and 1 (including 0, excluding 1), round rounding3 ,Array arrayObject:
Method to create an array 1: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 变量名 = new Array("元素1","元素2"...); 给数组指定元素创建数组 的对象。
方式4:
var 变量名 = ["元素1","元素2"...];
数组要注意的细节:
1. 在javascript中数组的长度是可以发生变化的。
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+"<br/>"); 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+"<br/>");
3.1数字的方法
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使用指定的分隔符把数组中的元素拼装成一个字符串返回。
var elements = arr1.join(",");
c、pop :移除数组中的最后一个元素并返回该元素。
d、push:将新元素添加到一个数组中,并返回数组的新长度值。
arr1.push("你好");
e、reverse(); 翻转数组的元素
f、slice指定数组 的开始索引值与结束索引值截取数组的元素,并且返回子数组。(包头不包尾)
var subArr = arr1.slice(1,2);
g、sort排序,排序的时候一定要传入排序的方法。(不传时默认是按照ASCII表排列)
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、splice第一个参数是开始删除元素的 索引值, 第二参数是删除元素的个数,往后的数据就是插入的元素(也可以不写)。
arr1.splice(1,1,"张三","李四","王五");
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