Question

我无法将参数传递给javascript array.prototype.findIndex（callback [，thisArg]）API。 javascript文档指定可以传递参数但我没有运气。这是API参考Array.prototype.findIndex()

我在API中看到了这种语法：

arr.findIndex(callback[, thisArg])

这是我当前的实现，但我不喜欢它使用全局创建的变量实现的方式，它不是简单的测试代码。

var vm = this; //angular context
//List of objects
vm.someList = [{storeId: "1", name:"Carmel", quantity:"25", orderNumber:"12345"},
		       {storeId: "2", name:"Chocolate", quantity:"25", orderNumber:"23456"},
		       {storeId: "3", name:"Vanilla", quantity:"25", orderNumber:"34567"},
		       {storeId: "4", name:"Cinnamon", quantity:"25", orderNumber:"45678"}];
		
//List of items marked with priority
vm.priorityList = [{storeId: "3", name:"Vanilla", quantity:"25", orderNumber:"34567", priority: "true"}];
		
//For loop finds index of criteria to perform operation on someList[i] element
for(var i =0; i < vm.priorityList.length; i++){
	//itemToFind created in global scope.
        vm.itemToFind = vm.priorityList[i];
	var index = vm.someList.findIndex(findPriorityIndex);
	//Don't worry about the operation being performed.
    console.log(index);
}

//callback fn used
function findPriorityIndex(element, index, array){
     return (element.storeId === vm.itemToFind.storeId
        && element.orderNumber ===vm.itemToFind.orderNumber);
}

我尝试使用以下语法将该参数传递给回调中的thisArg，但都导致尝试失败。我也承认API提到参数将在回调中被引用，并且我在回调函数中进行了这样的调整。

vm.someList.findIndex(findPriorityIndex[, vm.priorityList[i]]);
vm.someList.findIndex(findPriorityIndex(vm.priorityList[i]));
vm.someList.findIndex([findPriorityIndex, vm.priorityList[i]]);

如果有人能提供关于如何将参数传递给回调函数的任何信息，我将非常感激。

Answer 1

基本上你在回调中设置了thisArg的findIndex，this。

for (var i = 0; i < vm.priorityList.length; i++) {
    index = vm.someList.findIndex(findPriorityIndex, vm.priorityList[i]);´
    //                                   set thisArg ^^^^^^^^^^^^^^^^^^
    console.log(index);
}

// callback fn used
function findPriorityIndex(element, index, array) {
    return element.storeId === this.storeId && element.orderNumber === this.orderNumber;
    //        access this here ^^^^                                and ^^^^
}

Answer 2

简单地说，使用 this 来访问参数，如下所述

const fruits = [{id:1,label:"apple"},{id:2,label: "banana"}, {id:3,label:"cantaloupe"}
            ];
function checkIndex(element) {

    return element.label == this;
}

console.log(fruits.findIndex(checkIndex,'banana'));

将参数传递给array.prototype.findIndex（callback [，thisArg]）

2 个答案: