引用类内的变量

Question

我是一个使用 javascript 的新手/来自 PHP 世界/所以请原谅我的无知。我无法访问this._targeta 中的变量fetchPartial()，也看不到我做错了什么。我的错误是TypeError: undefined is not an object (evaluating 'this._target')你能帮我吗？'use strict';class View {    constructor(partial, target) {        this._partial = partial        this._target = target;    }        fetchPartial() {        fetch(this._partial).then(function (response) {            // The API call was successful!            return response.text();        }).then(function (html) {            let elem = document.querySelector( this._target ) // error: TypeError: undefined is not an object (evaluating 'this._target')            elem.innerHTML = html        }).catch(function (err) {            // There was an error            console.warn('Something went wrong.', err);        });    }}let p = new View('/_partial.html', '#_partial');p.fetchPartial();

Answer 1

代替：

fetchPartial() {

        fetch(this._partial).then(function (response) {

            // The API call was successful!

            return response.text();

        }).then(function (html) {

            let elem = document.querySelector( this._target ) // error: TypeError: undefined is not an object (evaluating 'this._target')

            elem.innerHTML = html

        }).catch(function (err) {

            // There was an error

            console.warn('Something went wrong.', err);

        });

    }

你应该做：

fetchPartial() {

        fetch(this._partial).then(function (response) {

            // The API call was successful!

            return response.text();

        }).then((html) => {

            let elem = document.querySelector( this._target ) // error: TypeError: undefined is not an object (evaluating 'this._target')

            elem.innerHTML = html

        }).catch(function (err) {

            // There was an error

            console.warn('Something went wrong.', err);

        });

    }

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