javascript / node.js中的JSONP解析

Question

If I have an string containing a JSONP response, for example "jsonp([1,2,3])" , and I want to retrieve the 3rd parameter 3 , how could I write a function that do that for me? I want to avoid using eval . My code (below) works fine on the debug line, but return undefined for some reason.

  function unwrap(jsonp) {
    function unwrapper(param) {
      console.log(param[2]); // This works!
      return param[2];
    }
    var f = new Function("jsonp", jsonp);
    return f(unwrapper);
  }

  var j = 'jsonp([1,2,3]);'

  console.log(unwrap(j)); // Return undefined

More info: I'm running this in a node.js scraper, using request library.

Here's a jsfiddle https://jsfiddle.net/bortao/3nc967wd/

Answer 1

Just slice the string to remove the jsonp( and ); , and then you can JSON.parse it:

 function unwrap(jsonp) { return JSON.parse(jsonp.slice(6, jsonp.length - 2)); } var j = 'jsonp([1,2,3]);' console.log(unwrap(j)); // returns the whole array console.log(unwrap(j)[2]); // returns the third item in the array 

Note that new Function is just as bad as eval .

Answer 2

Just a little changes and it'll work fine:

function unwrap(jsonp) {
    var f = new Function("jsonp", `return ${jsonp}`);
    console.log(f.toString())
    return f(unwrapper);
}

function unwrapper(param) {
    console.log(param[2]); // This works!
    return param[2];
}

var j = 'jsonp([1,2,3]);'
console.log(unwrap(j)); // Return undefined

without return your anonymous function is like this :

function anonymous(jsonp) {
    jsonp([1,2,3]);
}

because this function doesn't return so the output will be undefined.