带有点/括号符号的LocalStorage获取项目不适用于JSON.parse() [英] LocalStorage Get Item with Dot/Bracket Notation Not Working with JSON.parse()
问题描述
如果可能，我希望能够使用速记符号从localStorage获取项目，然后在其上使用JSON.parse().
If possible, I would like to be able to use shorthand notation to get an item from localStorage and then use JSON.parse() on it.
在下面的代码中，如果我使用以下代码，它将起作用:
In my code below, if I use the following it works:
var retrievedObject = JSON.parse(localStorage.getItem('testObject')); //works
但是，如果我使用以下两个速记选项之一，则它不起作用:
However, if I use one of the two following shorthand options, it doesn't work:
var retrievedObject = JSON.parse(localStorage.testObject); //doesn't work
var retrievedObject = JSON.parse(localStorage['testObject']); //doesn't work
我所有的代码都在jsFiddle下方和上: http://jsfiddle.net/TestB/1/.
All of my code is below and on jsFiddle: http://jsfiddle.net/TestB/1/.
//var retrievedObject = JSON.parse(localStorage.getItem('testObject')); //works
var retrievedObject = JSON.parse(localStorage.testObject); //doesn't work
//var retrievedObject = JSON.parse(localStorage['testObject']); //doesn't work
if (retrievedObject == null) {
var testObject = { 'one': 1, 'two': 2, 'three': 3 };
// Put the object into storage
localStorage.testObject = JSON.stringify(testObject);
}
else {
retrievedObject.four = 4;
// Put the object into storage
localStorage.testObject = JSON.stringify(retrievedObject);
}
// Retrieve the object from storage
var retrievedObject = JSON.parse(localStorage.getItem('testObject'));
console.log('retrievedObject: ', retrievedObject);
推荐答案
第一次未定义localStorage.testObject时会发生此问题.
The problem occurs the first time, when the localStorage.testObject is not yet defined..
在这种情况下，localStorage.testObject是未定义的，而JSON.parse失败并带有该参数
In that case localStorage.testObject is undefined and JSON.parse fails with that argument
另一方面，getItem方法在内部进行处理并返回null.
On the other hand the getItem method handles this internally and returns null..
您可以使用JSON.parse(localStorage.testObject || null)
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