JavaScript

# Functions as Data

```// We define some simple functions here
function add(x,y) { return x + y; }
function subtract(x,y) { return x - y; }
function multiply(x,y) { return x * y; }
function divide(x,y) { return x / y; }

// Here's a function that takes one of the above functions
// as an argument and invokes it on two operands
function operate(operator, operand1, operand2)
{
return operator(operand1, operand2);
}

// We could invoke this function like this to compute the value (2+3) + (4*5):
var i = operate(add, operate(add, 2, 3), operate(multiply, 4, 5));

// For the sake of the example, we implement the functions again, this time
// using function literals within an object literal;
var operators = {
add:      function(x,y) { return x+y; },
subtract: function(x,y) { return x-y; },
multiply: function(x,y) { return x*y; },
divide:   function(x,y) { return x/y; },
pow:      Math.pow  // Works for predefined functions too
};

// This function takes the name of an operator, looks up that operator
// in the array, and then invokes it on the supplied operands. Note
// the syntax used to invoke the operator function.
function operate2(op_name, operand1, operand2)
{
if (typeof operators[op_name] == "function")
return operators[op_name](operand1, operand2);
else throw "unknown operator";
}

// We could invoke this function as follows to compute
// the value ("hello" + " " + "world"):
var j = operate2("add", "hello", operate2("add", " ", "world"))
// Using the predefined Math.pow() function:
var k = operate2("pow", 10, 2)
```
i;

j;

k;

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