Is there a way to get the function parameter names of a function dynamically?

Let’s say my function looks like this:

function doSomething(param1, param2, .... paramN){
   // fill an array with the parameter name and value
   // some other code 
}

Now, how would I get a list of the parameter names and their values into an array from inside the function?

标签： javascript reflection function-parameter

30条回答

浅入江南

2楼-- · 2018-12-31 06:03

I don't know if this solution suits your problem, but it lets you redefine whatever function you want, without having to change code that uses it. Existing calls will use positioned params, while the function implementation may use "named params" (a single hash param).

I thought that you will anyway modify existing function definitions so, why not having a factory function that makes just what you want:

<!DOCTYPE html>

<html>
<head>
<meta charset="UTF-8">
<title></title>
<script type="text/javascript">
var withNamedParams = function(params, lambda) {
    return function() {
        var named = {};
        var max   = arguments.length;

        for (var i=0; i<max; i++) {
            named[params[i]] = arguments[i];
        }

        return lambda(named);
    };
};

var foo = withNamedParams(["a", "b", "c"], function(params) {
    for (var param in params) {
        alert(param + ": " + params[param]);
    }
});

foo(1, 2, 3);
</script>
</head>
<body>

</body>
</html>

Hope it helps.

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栀子花@的思念

3楼-- · 2018-12-31 06:03

I have read most of the answers here, and I would like to add my one-liner.

new RegExp(Function.name+'\\s*\\((.*?)\\)').exec(Function.toString().replace(/\n/g, ''))[1].replace(/\/\*.*?\*\//g, '').replace(/ /g, '')

function getParameters(func) {
  return new RegExp(func.name+'\\s*\\((.*?)\\)').exec(func.toString().replace(/\n/g, ''))[1].replace(/\/\*.*?\*\//g, '').replace(/ /g, '');
}

or for a one-liner function in ECMA6

var getParameters = func => new RegExp(func.name+'\\s*\\((.*?)\\)').exec(func.toString().replace(/\n/g, ''))[1].replace(/\/\*.*?\*\//g, '').replace(/ /g, '');

Let's say you have a function

function foo(abc, def, ghi, jkl) {
  //code
}

The below code will return "abc,def,ghi,jkl"

That code will also work with the setup of a function that Camilo Martin gave:

function  (  A,  b
,c      ,d
){}

Also with Bubersson's comment on Jack Allan's answer:

function(a /* fooled you)*/,b){}

Explanation

`new RegExp(Function.name+'\\s\\((.?)\\)')`

This creates a Regular Exponent with the new RegExp(Function.name+'\\s*\\((.*?)\\)'). I have to use new RegExp because I am injecting a variable (Function.name, the name of the function being targeted) into the RegExp.

Example If the function name is "foo" (function foo()), the RegExp will be /foo\s*\((.*?)\)/.

`Function.toString().replace(/\n/g, '')`

Then it converts the entire function into a string, and removes all newlines. Removing newlines helps with the function setup Camilo Martin gave.

`.exec(...)[1]`

This is the RegExp.prototype.exec function. It basically matches the Regular Exponent (new RegExp()) into the String (Function.toString()). Then the [1] will return the first Capture Group found in the Regular Exponent ((.*?)).

`.replace(/\/\.?\*\//g, '').replace(/ /g, '')`

This will remove every comment inside /* and */, and remove all spaces.

If you want to make all the parameters into an Array instead of a String separated by commas, at the end just add .split(',').

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皆成旧梦

4楼-- · 2018-12-31 06:04

I've tried doing this before, but never found a praticial way to get it done. I ended up passing in an object instead and then looping through it.

//define like
function test(args) {
    for(var item in args) {
        alert(item);
        alert(args[item]);
    }
}

//then used like
test({
    name:"Joe",
    age:40,
    admin:bool
});

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浮光初槿花落

5楼-- · 2018-12-31 06:06

This package uses recast in order to create an AST and then the parameter names are gathered from their, this allows it to support pattern matching, default arguments, arrow functions and other ES6 features.

https://www.npmjs.com/package/es-arguments

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路过你的时光

6楼-- · 2018-12-31 06:07

I'll give you a short example below:

function test(arg1,arg2){
    var funcStr = test.toString()
    var leftIndex = funcStr.indexOf('(');
    var rightIndex = funcStr.indexOf(')');
    var paramStr = funcStr.substr(leftIndex+1,rightIndex-leftIndex-1);
    var params = paramStr.split(',');
    for(param of params){
        console.log(param);   // arg1,arg2
    }
}

test();

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梦该遗忘

7楼-- · 2018-12-31 06:08

Here is an updated solution that attempts to address all the edge cases mentioned above in a compact way:

function $args(func) {  
    return (func + '')
      .replace(/[/][/].*$/mg,'') // strip single-line comments
      .replace(/\s+/g, '') // strip white space
      .replace(/[/][*][^/*]*[*][/]/g, '') // strip multi-line comments  
      .split('){', 1)[0].replace(/^[^(]*[(]/, '') // extract the parameters  
      .replace(/=[^,]+/g, '') // strip any ES6 defaults  
      .split(',').filter(Boolean); // split & filter [""]
}

Abbreviated test output (full test cases are attached below):

'function (a,b,c)...' // returns ["a","b","c"]
'function ()...' // returns []
'function named(a, b, c) ...' // returns ["a","b","c"]
'function (a /* = 1 */, b /* = true */) ...' // returns ["a","b"]
'function fprintf(handle, fmt /*, ...*/) ...' // returns ["handle","fmt"]
'function( a, b = 1, c )...' // returns ["a","b","c"]
'function (a=4*(5/3), b) ...' // returns ["a","b"]
'function (a, // single-line comment xjunk) ...' // returns ["a","b"]
'function (a /* fooled you...' // returns ["a","b"]
'function (a /* function() yes */, \n /* no, */b)/* omg! */...' // returns ["a","b"]
'function ( A, b \n,c ,d \n ) \n ...' // returns ["A","b","c","d"]
'function (a,b)...' // returns ["a","b"]
'function $args(func) ...' // returns ["func"]
'null...' // returns ["null"]
'function Object() ...' // returns []

function $args(func) {  
    return (func + '')
      .replace(/[/][/].*$/mg,'') // strip single-line comments
      .replace(/\s+/g, '') // strip white space
      .replace(/[/][*][^/*]*[*][/]/g, '') // strip multi-line comments  
      .split('){', 1)[0].replace(/^[^(]*[(]/, '') // extract the parameters  
      .replace(/=[^,]+/g, '') // strip any ES6 defaults  
      .split(',').filter(Boolean); // split & filter [""]
}  

// test cases  
document.getElementById('console_info').innerHTML = (
[  
  // formatting -- typical  
  function(a,b,c){},  
  function(){},  
  function named(a, b,  c) {  
/* multiline body */  
  },  
    
  // default values -- conventional  
  function(a /* = 1 */, b /* = true */) { a = a||1; b=b||true; },  
  function fprintf(handle, fmt /*, ...*/) { },  
  
  // default values -- ES6  
  "function( a, b = 1, c ){}",  
  "function (a=4*(5/3), b) {}",  
  
  // embedded comments -- sardonic  
  function(a, // single-line comment xjunk) {}
    b //,c,d
  ) // single-line comment
  {},  
  function(a /* fooled you{*/,b){},  
  function /* are you kidding me? (){} */(a /* function() yes */,  
   /* no, */b)/* omg! */{/*}}*/},  
  
  // formatting -- sardonic  
  function  (  A,  b  
,c  ,d  
  )  
  {  
  },  
  
  // by reference  
  this.jQuery || function (a,b){return new e.fn.init(a,b,h)},
  $args,  
  
  // inadvertent non-function values  
  null,  
  Object  
].map(function(f) {
    var abbr = (f + '').replace(/\n/g, '\\n').replace(/\s+|[{]+$/g, ' ').split("{", 1)[0] + "...";
    return "    '" + abbr + "' // returns " + JSON.stringify($args(f));
  }).join("\n") + "\n"); // output for copy and paste as a markdown snippet

<pre id='console_info'></pre>

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How to get function parameter names/values dynamic

Explanation

new RegExp(Function.name+'\\s*\\((.*?)\\)')

Function.toString().replace(/\n/g, '')

.exec(...)[1]

.replace(/\/\*.*?\*\//g, '').replace(/ /g, '')

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`new RegExp(Function.name+'\\s\\((.?)\\)')`

`Function.toString().replace(/\n/g, '')`

`.exec(...)[1]`

`.replace(/\/\.?\*\//g, '').replace(/ /g, '')`