数据函数(Functions as Data)

最新推荐文章于 2024-07-27 19:12:42 发布

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最新推荐文章于 2024-07-27 19:12:42 发布

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分类专栏： javascript 文章标签： JavaScript UP J# ViewUI

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本文通过具体的示例展示了如何在JavaScript中使用函数式编程的概念，包括定义简单的数学运算函数、利用高阶函数进行操作以及通过对象字面量来管理不同的运算符。

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  <script>
// 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 simple 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 object, 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)

alert(k);

</script>

OReilly.JavaScript.The.Definitive.Guide.5th.Edition.Aug.2006.chm：
能过函数operate2的调用函数列表operators，调用方式为operators[op_name](operand1, operand2);这样进行嵌入(invoke)函数