JSON.parse to an object array

Question

I'm having a difficult time with something that should be (and probably is) pretty basic. I have a constructor as follows:

function search_table(v1, v2, v3) {
    this.field = v1;
    this.condition = v2;
    this.value = v3;
}

My application has an array of search_table which gets JSON.stringify(ied) and then stored in localStorage.

My question is... when I retrieve the object from localStorage, it's in JSON string format. How do I get it back into the search_table[] format?

I'd prefer to do this without jQuery if possible. Thanks

I've tried to use something like the following:

var search_array = JSON.parse(string_val);

But it doesn't allow me to access search_array[i].condition as an example.

This should work. Please provide an example of what you're getting back in string_val. — ziesemer
– ziesemer, Commented Jan 21, 2012 at 20:10
When I do: alert(search_array) it looks the same as the JSON (I assume this is normal). In the JavaScript console it says 'Uncaught TypeError: Cannot read property 'condition' of undefined.' — joelc
– joelc, Commented Jan 21, 2012 at 20:14
Note: Some browsers do not support JSON.stringify, perhaps this could be affecting your application. — Travis J
– Travis J, Commented Jan 21, 2012 at 20:16
Travis - JSON.stringify and JSON.parse both work as expected (outputs are below). — joelc
– joelc, Commented Jan 21, 2012 at 21:30

ziesemer · Accepted Answer · 2012-01-21 20:17:15Z

2

This should work. The following code:

function search_table(v1, v2, v3) {
    this.field = v1;
    this.condition = v2;
    this.value = v3;
}
var arr = [new search_table(1, 2, 3), new search_table(4, 5, 6), new search_table(7, 8, 9)];

var str = JSON.stringify(arr);
console.log("stingified: ", str);

var search_array = JSON.parse(str);
var result = search_array[1].condition;
console.log("result: ", result);

Gives the following output:

stingified: [{"field":1,"condition":2,"value":3},{"field":4,"condition":5,"value":6},{"field":7,"condition":8,"value":9}]
result: 5

Your issue is elsewhere in the code that you haven't included here.

I'd also check Travis's suggestion - does your browser have native support for the JSON functions? Try these, and make sure they don't return "undefined":

alert(JSON.stringify);
alert(JSON.parse);

Also, make sure you initialized i, and that it is in-bounds of your array.

answered Jan 21, 2012 at 20:17

ziesemer

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5 Comments

joelc Over a year ago

Thanks Ziesemer. I noticed when I alert(search_array) from my code above it shows the JSON string, but when I alert(search_array) from your example, it shows [object Object],[object Object],[object Object]. alert(JSON.stringify) returns function stringify() { [native code] } as expected, as does alert(JSON.parse). Any ideas?

joelc Over a year ago

I just tried alert(search_array[0]) from mine and it is treating search_array like a string. i.e. search_array[0] = '[', 1 is '{', 2 is '"', 3 is 'f', and so on.

ziesemer Over a year ago

@haxor - Please output and provide an actual example of what you're seeing in your read string. Clearly, something isn't right here. Showing all of the [object Object] just means that your browser doesn't have the best toString implementation on Array, but everything is still as expected.

joelc Over a year ago

I figured it out, and it's strange. I had to JSON.parse(JSON.parse(...)) my variable for some reason. When I call into my local_storage_persist_object (which is a localStorage.setItem wrapper), I'm performing a JSON.stringify on its val. I'm wondering if localStorage.getItem doesn't automatically perform a JSON.parse. Any idea? FWIW the first time I perform a JSON.parse and the second time I perform a JSON.parse, the values are the same, but in the first case the quotes are escaped, whereas they are not in the second.

ziesemer Over a year ago

@haxor - I think I'd need to see your complete code to understand - but I'm glad you figured it out.

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