reduce 函数很容易转换成 async function,但并行性却很难搞清楚。幸运的是,它很少破坏任何东西。 但在一些资源密集型或速度限制的情况下,了解函数的调用方式是至关重要的。
let sum= arr.reduce(function(prev, cur, index, arr) { console.log(prev, cur, index);returnprev +cur; })//报错,"TypeError: Reduce of empty array with no initial value" 但是要是我们设置了初始值就不会报错,如下: //空数组,但设置 初始值 的情况let arr =[]; let sum= arr.reduce(functi...
let arr = [[0, 1], [2, 3], [4,[5,6,7]]] const newArr =function(arr){ returnarr.reduce((pre,cur)=>pre.concat(Array.isArray(cur)?newArr(cur):cur),[]) } console.log(newArr(arr));//[0, 1, 2, 3, 4, 5, 6, 7] (4)、对象里的属性求和 varresult = [ { subject:'...
Array.prototype.reduce() 是JavaScript 中的一个高阶函数,用于将数组中的元素通过一个累加器函数累积成一个单一的值。在计算对象数组中元素的出现次数时,reduce() 函数非常有用。 基础概念 reduce() 方法接收两个参数: 回调函数(reducer function),它本身接收四个参数: 累加器(accumulator),累积回调的返回值。 ...
const sum = arr.reduce(function(accumulator, currentValue, currentIndex, array){ console.log(accumulator, currentValue, currentIndex, array) return accumulator + currentValue }, 0) // 执行顺序 // 0 0 0 (5) [0, 1, 2, 3, 4] // 0 1 1 (5) [0, 1, 2, 3, 4] ...
prototype.flat2 = function (n = 1) { const len = this.length let count = 0 let current = this if (!len || n === 0) { return current } // Confirm whether there are array items in current const hasArray = () => current.some((it) => Array.isArray(it)) // Expand one ...
print_r(array_reduce($a,"myfunction")); ?> Try it Yourself » Definition and Usage The array_reduce() function sends the values in an array to a user-defined function, and returns a string. Note:If the array is empty and initial is not passed, this function returns NULL. ...
Reduces an array to an accumulated value by applying a LAMBDA function to each value and returning the total value in the accumulator
<?phpfunctioncall_back_function($v1,$v2){return$v1."-".$v2;}$input=array("a"=>"banana","b"=>"apple","c"=>"orange");print_r(array_reduce($input,call_back_function));print_r("");print_r(array_reduce($input,call_back_function,10));?> This will...
//假如运行下段reduce()代码:[0,1,2,3,4].reduce(function(accumulator, currentValue, currentIndex, array){returnaccumulator +currentValue; }); 1. 2. 3. 4. callback 被调用四次,每次调用的参数和返回值如下表 由reduce返回的值将是最后一次回调返回值(10)。你还可以使用箭头函数来代替完整的函数。