自定义过滤器提供“无法读取未定义的属性‘切片’"在 AngularJS 中 [英] Custom filter giving "Cannot read property 'slice' of undefined" in AngularJS

问题描述

我的自定义 startFrom 过滤器给我一个错误.

My custom startFrom filter is giving me an error.

app.filter('startFrom', function() {
    return function(input, start) {
        start = +start; //parse to int
        return input.slice(start);
    }
});

app.controller("PostCtrl", function($scope, $http) {
$scope.currentPage = 0;
$scope.pageSize = 10;
$scope.hidePagination = true;

$scope.search = function() {
    $http.get('someurl').then(sucesscalback,errorcalback);
    function sucesscalback(response)
    {
        $scope.hidePagination = false;
        console.log("Success:");
        console.log(response.data.records);
        $scope.posts = response.data;
        $scope.numberOfPages=Math.ceil($scope.posts.records.length/$scope.pageSize); 
        alert($scope.numberOfPages);
    }
    function errorcalback(failure)
    {
        console.log("Error:");
        console.log(failure);
    }

推荐答案

你的过滤器需要检查输入是否存在:

Your filter needs to check whether or not the input exists:

app.filter('startFrom', function() {
    return function(input, start) {
        if (!input || !input.length) { return; }
        start = +start; //parse to int
        return input.slice(start);
    }
});

否则，过滤器函数将运行并因此在 undefined 上调用 slice ，它没有 slice 的属性，如数组或字符串可以.

Otherwise, the filter function will run and thus call slice on undefined which doesn't have a property of slice like an array or string does.

过滤器在没有值时被调用的原因是过滤器会在 Angular 运行它的第一个 $digest 循环时运行.您可以通过在控制器中添加初始值来避免该错误，但最好仅将 if 语句添加到过滤器中.

The reason the filter is called while there is no value is because the filter will run when Angular runs its first $digest cycle. You could avoid the error by adding an initial value in the controller, but it's best just to add the if statement to the filter.

这是两种解决方案的演示.注意没有错误.

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