如何在没有try / catch的情况下检查对象是否具有特定键

Question

我从服务器收到此JSON，我需要检查它是否包含密钥read.nores

如果我这样做

if (data[0]["read.nores"]) {
    return;
}

它会崩溃，因为它不包含该密钥。

如何在没有try / catch方法的情况下检查密钥是否存在，例如.has（＆＃34; read.nores＆＃34;）？

Answer 1

它不会崩溃。 如果检查对象的任何属性，并且未在对象中定义它，则默认为undefined。所以你的if条件会完美运作。

Answer 2

安全地读取未定义的密钥会产生(function (global) { System.config({ paths: { // paths serve as alias 'npm:': 'node_modules/' }, // map tells the System loader where to look for things map: { // our app is within the app folder app: 'app', // angular bundles '@angular/core': 'npm:@angular/core/bundles/core.umd.js', '@angular/common': 'npm:@angular/common/bundles/common.umd.js', '@angular/compiler': 'npm:@angular/compiler/bundles/compiler.umd.js', '@angular/platform-browser': 'npm:@angular/platform-browser/bundles/platform-browser.umd.js', '@angular/platform-browser-dynamic': 'npm:@angular/platform-browser-dynamic/bundles/platform-browser-dynamic.umd.js', '@angular/http': 'npm:@angular/http/bundles/http.umd.js', '@angular/router': 'npm:@angular/router/bundles/router.umd.js', '@angular/router/upgrade': 'npm:@angular/router/bundles/router-upgrade.umd.js', '@angular/forms': 'npm:@angular/forms/bundles/forms.umd.js', '@angular/upgrade': 'npm:@angular/upgrade/bundles/upgrade.umd.js', '@angular/upgrade/static': 'npm:@angular/upgrade/bundles/upgrade-static.umd.js', // other libraries 'rxjs': 'npm:rxjs', 'angular-in-memory-web-api': 'npm:angular-in-memory-web-api/bundles/in-memory-web-api.umd.js', 'ng2-ckeditor': 'npm:ng2-ckeditor', }, // packages tells the System loader how to load when no filename and/or no extension packages: { app: { main: './main.js', defaultExtension: 'js' }, 'ng2-ckeditor': { defaultExtension: 'js' }, rxjs: { defaultExtension: 'js' } } map: { "ng2-ckeditor": "node_modules/ng2-ckeditor/lib/ckeditor.component.js" } }); })(this); ，但是从undefined读取密钥会抛出，因此问题将明确表示undefined不存在，而不是{ {1}}不存在。

要检查，请将其更改为：

data[0]