JSON.parse gives SyntaxError inside a for loop with array

Question

I have an array with direction renderer json's which are stringified.

array[1].direction = '{\"routes\":[{\"bounds\":\"\....'
array[1].direction = '{\"routes\":[{\"bounds\":\"\....'
.
.

This is what i did to render those json's on my map.

for (var x=2; x<array.length; x++) {

        renderDirections(array[x].direction);
    }

function renderDirections(result){

     var directionRenderer = new google.maps.DirectionsRenderer();

       myDirections = JSON.parse(result, function(name, value){

         if(/^LatLngPlaceHolder\(/.test(value)) { 
                    var match = /LatLngPlaceHolder\(([^,]+),([^,]+)\)/.exec(value);
                    return new google.maps.LatLng(match[1], match[2]);
                } 
         else{
           return value;
         }
        });

      directionRenderer.setMap(map);
      directionRenderer.setDirections(myDirections);
      directionRenderer.setOptions({suppressMarkers:true,preserveViewport:true});
    }

Doing this gives a "Uncaught SyntaxError: Unexpected token \" error at the JSON.parse line.

However, if i do:

for (var x=2; x<array.length; x++) {

        var examplejson = '{\"routes\":[{\"bounds\":\"\....'; //note that its an example json which i logged from `array[x].direction`
        renderDirections(examplejson);
    }

it renders the json.

Why are you escaping the quotes? It's a javascript object, it has to contain quotes to identify properties. It's not a string. — Rob
– Rob, Commented Apr 18, 2013 at 16:59

PaulProgrammer · Accepted Answer · 2013-04-18 16:59:20Z

2

The \ is only needed when you're creating the JSON inside a string to be parsed into an object. Remove \ from your first example and you'll have better luck.

array[1].direction = {"routes":[{"bounds":"....

The \ tells the parser that "don't treat the quote as a terminator, but as a character." Outside a quoted string, it's just incorrect.

answered Apr 18, 2013 at 16:59

PaulProgrammer

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7 Comments

Felix Kling Over a year ago

One could argue that the OP has a string in the example (last code snippet).

PaulProgrammer Over a year ago

sigh yes we all write in strings. But some are treated by the parser as "string types" and others as "syntactical units". The first example, the OP is creating a JSON object as a syntactical unit, in the second, he's created a string that is parsed in to a JSON object.

hackio Over a year ago

Sorry but i couldn't understand what you mean. it is the same string in the array and in the second example. but when i assign it to a var (the same string with backslash) instead of an array it works.

Ian Over a year ago

@PaulProgrammer If this were true, you'd get an error a lot sooner than the parse. var obj = {\"key\": []}; = "Unexpected token ILLEGAL"

Felix Kling Over a year ago

Well yeah, I'm not talking about the first example but the code the OP seems to actually run (the last part). And again, there is no such thing as a JSON object. What you are referring to are object initializers or object literals in JS. JSON is a textual data exchange format.

|

praneetloke · Accepted Answer · 2013-04-18 17:36:31Z

You shouldn't have to create the direction objects that way. If you are constructing a dynamic json then you should do something like this:

var array = [];
var obj = {
   key: "value",
   key2: "value2",
   key3: 3
};
array.push(obj);

If you receive the value for key and key2 from a server then you can just substitute the hard-coded string with the variable containing the value. Coding your objects in the above manner is easier to maintain too. It's horrendous to write a manually encoded json object. You'll never know what mistakes will creep in when you edit them. If you need to serialize that array for storage you can just JSON.stringify(array) and that will return a json encoded string that you can transmit over the wire or even store in localStorage.

With the approach I showed you, you wouldn't need a JSON.parse at all so you save yourself from calling JSON.parse in a loop unnecessarily. If you have a different reason for creating the json object like the way you are, you should probably state that in your question. But either way, you shouldn't have to do that.

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