It seems like there are some issues with the single and double quote characters in your code, possibly due to a copy and paste error. The JSON format you've provided is correct for creating an array of objects, just make sure to remove the unnecessary double quotes.
To test this out, you can use Chrome's JavaScript console and paste the following code:
var myVar = [{'x': 1, 'b': 2}, {'x': 100, 'b': 200}]
// Now myVar will contain an array of two objects.
// Try accessing one of the object properties to verify it works.
myVar[0].b
UPDATE
If the browser supports ECMAScript 5, you can utilize the built-in JSON.parse function.
// Your JSON data
var myJson = '[{"x": 1, "b": 2}, {"x": 100, "b": 200}]';
// Call a custom function parseJson to parse the JSON data and store the results in parsedObject variable.
var parsedObject = parseJson(myJson);
function parseJson(json) {
return JSON.parse(json);
}