section7.7.md

Section 7.7: Monkey patch a function into an existing class

Sometimes it's useful to be able to extend a class with new functions. For example let's suppose that a string should be converted to a camel case string. So we need to tell TypeScript, that String contains a function called toCamelCase , which returns a string .

interface String {
  toCamelCase(): string;
}

Now we can patch this function into the String implementation.

String.prototype.toCamelCase = function() : string {
  return this.replace(/[^a-z ]/ig, '')
    .replace(/(?:^\w|[A-Z]|\b\w|\s+)/g, (match: any, index: number) => {
      return + match === 0 ? "" : match[index === 0 ? 'toLowerCase' : 'toUpperCase']();
    });
}

If this extension of String is loaded, it's usable like this:

"This is an example".toCamelCase(); // => "thisIsAnExample"