JS : how to convert a string to JS Object (**NOT** to JSON)?

Question

I know how to parse a valid JSON string : JSON.parse('{"key" : "value"}') .

But what about a valid JS object, but invalid JSON , like : JSON.parse("{ key : 'value'}") ? The example above throws :

Uncaught SyntaxError: Unexpected token k in JSON at position 2

My actual goal is even trickier. I want to parse a string of a JS object containing RegEx (unsupported by JSON but supported by JS) into a JS object :

'{ key1 : /val1/g , key2 : /val2/i }'

I eventually want to use this object with Mongoose and find documents with it :

Model.find({
     key1 : /val1/g ,
     key2 : /val2/i
})

I have tried applying a fairly complex RegEx to my String, replacing /val1/g with new RegEx("val1","i") :

str = str.replace( /\/(.+?)\/(g?i?).+?(?=,|})/g , "new RegExp(`$1`,`$2`)" )

The .replace() operation works and modifies the string the way I want it. It yields :

{ key1 : new RegExp("val1","g") , key2 : new RegExp("val2","i") }

But when I try to apply JSON.parse to it, it still fails because new RegEx("val1","i") is not a valid value.

Answer 1

If you control and can trust the text you're converting, you can use eval :

 var str = '{ key1 : /val1/g , key2 : /val2/i }'; var obj = eval("(" + str + ")"); console.log(obj.key1); 

Note that when doing the eval , since your expression starts with { , you have to wrap it in () so the parser knows that's starting an object initializer, not a block.

A couple of notes about eval :

1. It allows arbitrary code execution. So you really have to trust the text you're eval ing. Don't eval user input.

2. Code in an execution context directly containing a call to eval basically cannot be optimized, because the JavaScript engine can't know, when parsing the code, what the string will contain. So while I suppose technically it's premature optimization, I'd tuck the above off in a function that you call from your main logic rather than embedding it in your main logic directly.