typescript - Property 'assign' does not exist on type 'ObjectConstructor'

Question

I am using TypeScript in my application, where I use function:

Object.assign(this.success, success.json())

However, during compilation, I receive the following error:

 error TS2339: Property 'assign' does not exist on type 'ObjectConstructor'.

Do you have any idea how can I get rid of this error?

Answer 1

Configure:

If you're using VS code (or if you see a tsconfig.json file):

You should add the lib property to your tsconfig.json and then your editor will use the bundled typescript type definitions and also give you intellisense.

Just add the "lib": ["esnext", "dom"] to your tsconfig.json and restart VS Code

{
    "compilerOptions": {
        // ...
        "target": "es5",
        "lib": ["esnext", "dom"]
        // ...
    }
}

See all tsconfig.json options here.

If you're using Visual Studio or MSBuild include this tag:

<TypeScriptLib>esnext, dom</TypeScriptLib>

See all MSBuild typescript compiler options and usage here.

---

Check your work:

If you've configured your project to use the built-in types and restarted your editor, then your resulting type will look like this instead of the type being any when you use Object.assign:

---

Note on polyfills and older browser compatibility:

Note that if you are transpiling to ES5 or lower and are targeting IE11, you will need to include polyfills because the typescript compiler will not include the polyfills for you.

If you'd like to include the polyfills (which you should) then I would recommend using core-js's polyfills.

npm install --save core-js

or

yarn add core-js

Then in the entry point in your app (e.g. /src/index.ts) add the import for core-js at the top of the file:

import 'core-js';

If you're not using a package manager then you can just paste the following polyfill taken from MDN in some place in your code that runs before the your usage of Object.assign.

if (typeof Object.assign != 'function') {
  // Must be writable: true, enumerable: false, configurable: true
  Object.defineProperty(Object, "assign", {
    value: function assign(target, varArgs) { // .length of function is 2
      'use strict';
      if (target == null) { // TypeError if undefined or null
        throw new TypeError('Cannot convert undefined or null to object');
      }

      var to = Object(target);

      for (var index = 1; index < arguments.length; index++) {
        var nextSource = arguments[index];

        if (nextSource != null) { // Skip over if undefined or null
          for (var nextKey in nextSource) {
            // Avoid bugs when hasOwnProperty is shadowed
            if (Object.prototype.hasOwnProperty.call(nextSource, nextKey)) {
              to[nextKey] = nextSource[nextKey];
            }
          }
        }
      }
      return to;
    },
    writable: true,
    configurable: true
  });
}