使用JSON时jQuery中if语句的说明

我正在学习《学习jQuery》一书中的jQuery，并发现部分代码不理解

JSON有一部分：

[
    {
        "term": "BACCHUS",
        "part": "n.",
        "definition": "A convenient deity invented by the...",
        "quote": [
            "Is public worship, then, a sin,",
            "That for devotions paid to Bacchus",
            "The lictors dare to run us in,",
            "And resolutely thump and whack us?"
        ],
        "author": "Jorace"
    },
    {
        "term": "BACKBITE",
        "part": "v.t.",
        "definition": "To speak of a man as you find him when..."
    },
    {
        "term": "BEARD",
        "part": "n.",
        "definition": "The hair that is commonly cut off by..."
    },

以下是jQuery代码：

$(document).ready(function() {
    $('#letter-b a').click(function() {
        $.getJSON('b.json', function(data) {
            $('#dictionary').empty();
            $.each(data, function(entryIndex, entry) {
                var html = '<div class="entry">';
                html += '<h3 class="term">' + entry['term'] + '</h3>';
                html += '<div class="part">' + entry['part'] + '</div>';
                html += '<div class="definition">';
                html += entry['definition'];
                if (entry['quote']) {
                    html += '<div class="quote">';
                    $.each(entry['quote'], function(lineIndex, line) {
                        html += '<div class="quote-line">' + line + '</div>';

---

另外，我试图搜索stackoverflow和Google，但找不到对此的解释。

您的JSON结构有一个可选键

quote

如果键存在，

entry['key']

在布尔上下文中计算为true（

If

）。如果它不存在，则计算为false，并且不执行后续的If块

因此，总结一下：

if (entry['quote']) {        // This block will only run if the JSON contains
                             //  a key "quote"
    html += '<div class="quote">';

---

JSON结构有一个可选键

quote

如果键存在，

entry['key']

在布尔上下文中计算为true（

If

）。如果它不存在，则计算为false，并且不执行后续的If块

因此，总结一下：

if (entry['quote']) {        // This block will only run if the JSON contains
                             //  a key "quote"
    html += '<div class="quote">';

---

entry

只是

$引用的匿名函数中的第二个参数。每个

。['quote']部分是用于引用特定属性（即键）的括号符号，在本例中，它似乎是

"quote": [
"Is public worship, then, a sin,",
"That for devotions paid to Bacchus",
"The lictors dare to run us in,",
"And resolutely thump and whack us?"]

---

entry

只是

$引用的匿名函数中的第二个参数。每个

。['quote']部分是用于引用特定属性（即键）的括号符号，在本例中，它似乎是

"quote": [
"Is public worship, then, a sin,",
"That for devotions paid to Bacchus",
"The lictors dare to run us in,",
"And resolutely thump and whack us?"]

if（entry['quote']）所做的全部工作是检查条目结构中是否存在此键。

if（entry['quote']）所做的全部工作是检查条目结构中是否存在此键