Question

如何让newData等于forEach()生成的对象数组？如果我全局定义var result = []和console.log(result);

，它就有效

var paragraphs = ["this is a p", "%%this is an h2", "%this is an h1"];

var newData = paragraphs.forEach(function(x) {
    var result = [];
    var header = 0;
    while (x.charAt(header) === "%")
     header++;

    if (header > 0) {
        result.push({type:"h" + header, content: x.slice(header)});
    } else { 
        result.push({type: "p", content: x}); 
    }
        return result;

});

console.log(newData); // undefined

Answer 1

forEach只是循环遍历数组 - 它不会创建新数组。 JavaScript中的Array原型的map函数循环遍历数组，执行您在回调函数中提供的逻辑，但返回一个给定回调的新数组，因为它的结果。您可以在MDN上阅读有关地图功能的更多信息：https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map

Answer 2

嘿@jamie你绝对应该考虑使用map()进行此操作。

虽然如果想使用forEach()，请尝试Immediately-Invoked Function Expression。它通常用于使用闭包来模拟私有方法。

看一下这段代码

var paragraphs = ["this is a p", "%%this is an h2", "%this is an h1"];

/* Using Immediately-Invoked Function Expression */
var newData = (function () {
    var result = []
    paragraphs.forEach(function (x) {
        var header = 0;
        while (x.charAt(header) === "%")
            header++;

        if (header > 0) {
            result.push({type: "h" + header, content: x.slice(header)});
        } else {
            result.push({type: "p", content: x});
        }
    });
    return result;
})();

console.log(newData);

/* Using Map */

var newestData = paragraphs.map(function (x) {
    var header = 0;
    while (x.charAt(header) === "%")
        header++;

    if (header > 0) {
        x = {type: "h" + header, content: x.slice(header)};
    } else {
        x = {type: "p", content: x};
    }
    return x;
});

console.log(newestData);

以下是jsfiddle。

将array.prototype.foreach（）的结果保存到未定义的变量中

2 个答案: