常用的JavaScript数组方法

//过滤年龄大于10的元素 
var ages = [5, 32, 7, 10, 33, 12, 40]; 
var res = ages.filter(function (currentValue) { 
  return currentValue > 10; 
}) 
console.log(res.toString()); 
//输出结果：32,33,12,40 
 
//箭头函数写法 
var res1 = ages.filter(item => item > 10) 
console.log(res.toString()); 

//循环输出每个参数 
var ages = [5, 32, 7, 10, 33, 12, 40]; 
ages.forEach(function (currentValue, index) { 
  console.log("参数:" + currentValue + "索引:" + index); 
}) 
 
 
//箭头函数写法 
ages.forEach((item, index) => { 
  console.log("参数:" + item + "索引:" + index); 
}) 

//把10修改成20 
var ages = [5, 32, 7, 10, 33, 12, 40]; 
ages.forEach(function (currentValue, index) { 
  if (currentValue === 10) { 
    ages[index] = 20 
    return 
  } 
  console.log(index); 
}) 
 
console.log(ages); 

//把10修改成20 
var ages = [5, 32, 7, 10, 33, 12, 40]; 
ages.some(function (currentValue, index) { 
  if (currentValue === 10) { 
    ages[index] = 20 
    return true 
  } 
  console.log(index); 
}) 
 
console.log(ages); 
 
//把10修改成20 箭头函数 
var ages = [5, 32, 7, 10, 33, 12, 40]; 
ages.some((item, index) => { 
  if (item === 10) { 
    ages[index] = 20 
    return true 
  } 
  console.log(index); 
}) 
 
console.log(ages); 

//判断每个元素的值是否都大于4 
var ages = [5, 32, 7, 10, 33, 12, 40]; 
 
 
var res = ages.some(function (currentValue) { 
  return currentValue > 4 
}) 
console.log(res); 
//输出：true 
 
//箭头函数 
var res = ages.some(item => item > 4) 
console.log(res); 

//计算所有元素的和 
var numbers = [15.5, 2.3, 1.1, 4.7]; 
var res = numbers.reduce(function (total, currentValue) { 
  return total += currentValue 
}, 0) 
 
console.log(res); 
//23.6 
 
//计算大于4的元素的和 
var result = numbers.filter(item => item > 4).reduce((total, item) => total += item, 0) 
console.log(result); 
//20.2 

var arr = [1, 2, 3] 
var arr2 = [4, 5, 6] 
 
var res = [...arr, ...arr2] 
console.log(res); 
//输出结果:[1, 2, 3, 4, 5, 6] 
 
var res = [...arr2, ...arr] 
console.log(res); 
//输出结果： [4, 5, 6, 1, 2, 3]