Home/ Questions/Cannot convert undefined or null to object - How can I circumvent the error?
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Delilah Wilson
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Asked: 2022-05-17T14:27:32+00:00 In:

Cannot convert undefined or null to object – How can I circumvent the error?

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I encountered the following problem in completing my work:

TypeError: Cannot convert undefined or null to object
  at Function.keys (native)
  at stringify (stringifyJSON.js:18:22)
  at stringifyJSON (stringifyJSON.js:27:13)
  at stringifyJSONSpec.js:7:20
  at Array.forEach (native)
  at Context.<anonymous> (stringifyJSONSpec.js:5:26)
  at Test.Runnable.run (mocha.js:4039:32)
  at Runner.runTest (mocha.js:4404:10)
  at mocha.js:4450:12
  at next (mocha.js:4330:14)

Below is the code I ran:

// five lines of comments
  var stringify = function(obj) {
  if (typeof obj === 'function') { return undefined;} // return undefined for function
  if (typeof obj === 'undefined') { return undefined;} // return undefined for undefined
  if (typeof obj === 'number') { return obj;} // number unchanged
  if (obj === 'null') { return null;} // null unchanged
  if (typeof obj === 'boolean') { return obj;} // boolean unchanged
  if (typeof obj === 'string') { return '"' + obj + '"';} // string gets escaped end-quotes
  if (Array.isArray(obj)) { 
  return obj.map(function (e) { // uses map() to create new array with stringified elements
  return stringify(e);
  });
  } else {
  var keys = Object.keys(obj); // convert object's keys into an array
  var container = keys.map(function (k) { // uses map() to create an array of key:(stringified)value pairs
  return k + ': ' + stringify(obj[k]);
  });
  return '{' + container.join(', ') + '}'; // returns assembled object with curly brackets
  }
 };
 
 var stringifyJSON = function(obj) {
  if (typeof stringify(obj) != 'undefined') {
  return "" + stringify(obj) + "";
  }
 };

What’s causing it, and how can it be resolved in the “cannot convert undefined or null to object“ in the javascript?

cannot convert undefined
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2 Answers

  1. Best Answer
    Expert

    The cause: When you call a function that expects an Object as an argument, however, it supplies undefined or null. This is the cause of the issue. For instance:

    Object.keys(null)
Object.assign(window.UndefinedVariable, {})

    Solution:

    The solution is to review your program and adjust the null/undefined condition so that the function either gets the right Object or is not called.

    Object.keys({'key': 'value'})
if (window.UndefinedVariable) {
Object.assign(window.UndefinedVariable, {})
}
    • 14

  2. Check that the destination object isn’t empty (null or undefined).

    This is how you can initialize destination objects with an empty object: 

    var destinationObj = {};

Object.assign(destinationObj, sourceObj);
    • 19

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