How to convert a JSON-like (not JSON) string to an object?

Question

We all know we can use JSON.parse() to convert the string '{"a":0,"b":"haha"}' to the object {a: 0, b: 'haha'}.

But can we convert the string '{a: 0, b: "haha"}' to the object {a: 0, b: 'haha'}?

I'm writing a web crawler and I need to get the data in the page. But the complete data is not in DOM but in one <script> element. So I got the useful content in the <script> and converted that string (like 'window.Gbanners = [{...}, {...}, {...}, ...];') to a JSON-like string (like '{banners : [...]}'). However, I couldn't parse the "JSON-like" string. Does anyone have a solution?

Possible duplicate of Convert JSON string to array of JSON objects in Javascript — abr
– abr, Commented Mar 5, 2018 at 14:12
Dare I suggest eval? (and simply get rid of the first and last ') — Adam Jenkins
– Adam Jenkins, Commented Mar 5, 2018 at 14:32
Are we fine with executing arbitrary code the scrapper might find on the internet? — Kos
– Kos, Commented Mar 6, 2018 at 9:05
@Kos No, we're not. I checked the script that I crawled and found it just did window.Gbanners=[];. Then I handled this script string simply and evaled it. Maybe I'm fine with it temporarily？ -^_^- — Li Enze
– Li Enze, Commented Mar 6, 2018 at 11:37

Kos · Accepted Answer · 2018-03-05 14:29:07Z

8

A string like {a: 0, b: "haha"} is not JSON, but just a bunch of JavaScript code.

Best way to get a JSON representation of data inside is to run it through a JS parser (such as Esprima), traverse the syntax tree and build a json object out of it. This needs some work, but at least you'll have the parsing done correctly, with proper handling of escape sequences.

Here's a starting point:

const esprima = require("esprima");
const code = '({a: 0, b: "haha"})';
const ast = esprima.parse(code);

const properties = ast.body[0].expression.properties;
const output = properties.reduce((result, property) => { 
  result[property.key.name] = property.value.value;
  return result;
}, {});
console.log(output);

This code assumes a lot about what the input code looks like - might be OK for a prototype, but still needs error checking and handling nested objects.

(A more generic approach could involve a recursive function that takes an ObjectExpression and returns an equivalent JSON.)

I also had to wrap your input in parentheses so that it's an expression (not a block statement) according to JS grammar.

edited Mar 5, 2018 at 14:29

answered Mar 5, 2018 at 14:16

Kos

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2 Comments

Li Enze Over a year ago

thanks! You mean I need to run the script in the <script>? Can you tell me about this more specifically? I'm using node.js.

Kos Over a year ago

No, you should just parse it, please don't run random scripts from the internet in your node environment :) Added example code to get you started

Shahbaz Shueb · Accepted Answer · 2018-03-05 14:43:21Z

4

Something like this might work:

function evalJsString(str) {
    let a = null;
    try {
        eval('a = ' + str);
    } catch (err) {
        console.error(err);
    }
    if(typeof a === "object")
      return a;
    else
      return null;
}

evalJsString('({a: 0, b: "haha"})');

answered Mar 5, 2018 at 14:43

Shahbaz Shueb

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1 Comment

Li Enze Over a year ago

When I planed to try to use a recursive way to handle more complex string after seeing @kos's answer, this simple and cool solution surprised me a lot!

Shuvojit Saha · Accepted Answer · 2020-06-17 20:26:08Z

0

As eval() has security flaws, it's better not to use it. A possible way would be creating a own parser to convert it to JSON string and then apply JSON.parse(). Something like below

function toJSONString(input) {
   const keyMatcher = '([^",{}\\s]+?)';
   const valMatcher = '(.,*)';
   const matcher = new RegExp(`${keyMatcher}\\s*:\\s*${valMatcher}`, 'g');
   const parser = (match, key, value) => `"${key}":${value}`
   return input.replace(matcher, parser);
}

JSON.parse(toJSONString('{a: 0, b: "haha"}'))

answered Jun 17, 2020 at 20:26

Shuvojit Saha

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