how to use the mixin function from the underscore library in javascript

The _.mixin function from the Underscore library allows you to add your own functions to the Underscore library in a way that allows them to be chained like regular Underscore functions. Here is an example of how to use it:

index.tsx
// Define your custom function, in this example a function that doubles a value
var double = function(num) {
  return num * 2;
};

// Add your custom function to the Underscore library
_.mixin({
  double: double
});

// Use your custom function like any other Underscore function, and chain it with other functions
var result = _.chain([1, 2, 3])
              .map(_.double)
              .map(function(num) { return num + 1; })
              .value();
// result will be [3, 5, 7]
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In the above example, we define a custom function double that doubles a given number. We then add this function to the Underscore library using the _.mixin function. This function takes an object as its parameter, where each key-value pair represents the name of the function being added and the function itself. Since we only want to add one function in this example, we pass a single object literal with the double function as its value.

Once we have added our custom function to Underscore, we can use it like any other Underscore function. In this example, we chain the _.map function to our array of numbers, first mapping each number to its double and then adding one to the result. The final result is [3, 5, 7].