Array to arguments function possible?

@JMRKERMay 08.2015

I see how the arguments of a function can be passed, displayed in and operated on in the following “findMax” function.

[code=php] <!DOCTYPE html> <html lang=”en”> <head> <meta charset=”UTF-8″ />

<title> HTML5 page </title>

</head> <body>

<script type=”text/javascript”> // Following from: http://www.w3schools.com/js/js_function_parameters.asp

function findMax() { // alert(‘findMax: ‘+[].join.call(arguments, ‘ : ‘)); // this demo shows arguments as an array var i, max = 0; for (i = 0; i < arguments.length; i++) { if (arguments[i] > max) { max = arguments[i]; } // shows arguments can be accessed } return max; } x = findMax(1, 123, 500, 115, 44, 88); alert(‘maximum: ‘+x);

// Trying to go the other way: Array to arguments pseudo-array tarr = [1,2,3,4,5,6,7,8,9]; function createArguments(tarr) { // alert(‘create: ‘+[].join.call(arguments, ‘ : ‘)); // this demo shows arguments as an array // for (var i=0; len=tarr.length, i<len; i++) { arguments.push(tarr[i]); } // cannot push an argument list return tarr.toString(); // creates a string same as .join() which is NOT an arguments display } var args = createArguments(tarr); alert(‘arguments: ‘+args); alert(‘maximum (version 2): ‘+findMax(args)); // returns 0 because there are no args for findMax function

</script>

</body> </html> [/code]

What I have NOT been able to accomplish, as tried above, is to go the other way:
Make an arguments (list, object, term?) from an array.

It this possible? Can an array be transferred into a arguments list and used in a different function?
?

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JavaScript

8 Comments(s) _↴

@mrhooMay 09.2015 — #Array's apply method uses the array passed as a second parameter as the arguments object of the function being applied to.

[CODE]function findMax(){
 var i, max= 0;
 for(i= 0; i<arguments.length; i++){
 if(arguments[i]>max){
 max= arguments[i];
 }
 }
 return max;
 }[/CODE]

[B]var x= [1, 123, 500, 115, 44, 88];

alert('maximum: '+findMax.apply(Array,x));[/B]

@JMRKERauthorMay 09.2015 — #Thanks for the answer, but that is not what I'm trying to find out about.

The 'findMax' function works OK as is and as far as I can see your version does the same thing.

What I trying to figure out is how to create the arguments list from an array.

For a non-working example:

max = findMax(1,2,3,4,5); // would return maximum value (5) of a list variable number of parameters.

I want to know if the list of parameters could be created like this

args = new Array(1,2,3,4,5); // allow any number of parameters

max = findMax(args); // where args would be the native values of 'arguments' within the function.

My guess at this time is that it can not be done.

Or that the function should be re-written to accept arrays (as you have done in your example provided) and NOT arguments

But if that is so, then why have the 'arguments' variable within any function of the JS language?

Maybe I'm just not asking the question the correct way?

But thanks for you alternate function demonstrating another way to "skin the cat" in JS.

@TcobbMay 09.2015 — #It can be done if you don't mind committing what is (to some people) the unpardonable sin of using 'eval'

[CODE]function speak(){  //just prints all args sent to it
 var i, z = arguments.length;
 for(i = 0; i < z; i++){
 console.log(arguments[i]);
 }
 
 }
 
 
 function many(fnc, arr){ //first arg is the function, second is the array to be converted into args
 var str, i, len, com;
 len = arr.length;
 str = '';
 for(i = 0; i < len; i++){
 if(typeof(arr[i]) === 'string'){  //to insure that string data is interpreted as string
 arr[i] = '"' + arr[i] + '"';
 }
 }
 str = arr.join(',');
 com = 'fnc(' + str + ')';
 eval(com);
 }
 
 many(speak,['alpha','beta','gamma', 44, 12]);
 [/CODE]

@JMRKERauthorMay 10.2015 — #Thanks "Tcobb". I'm not sure how useful the technique or function would be since .apply() and .call() are available in most browsers.

I was just interested in knowing

if the arguments could be converted [B]to[/B] an array [B]from[/B] the function arguments

what the [B]reverse action[/B] (to arguments from and array) would look like or if was possible to be done.

@ryanpillerinMay 10.2015 — #You mean like this?

[CODE]
 <!DOCTYPE html>
 <html>
 <body>
 
 <p>Finding the largest number.</p>
 <p id="demo"></p>
 
 <script>
 function findMax() {
 var i, max = 0;
 console.log(arguments);
 for(i = 0; i < arguments[0].date.length; i++) {
 if (arguments[0].date[i] > max) {
 max = arguments[0].date[i];
 }
 }
 return max;
 } 
 document.getElementById("demo").innerHTML = findMax({date: [1,2,3,4]});
 </script>
 
 </body>
 </html>
 [/CODE]

@JMRKERauthorMay 10.2015 — #Yes, that makes sense now, but I never would have come up with it myself.

I modified your code a bit because the 'date' parameter threw me off for a bit.

I also show that both literal array can be used with literal parameters

as well as with a variable array assignment.

Neat. Thank you 'ryanpillerin'

[code=php]
 <!DOCTYPE html>
 <html>
 <body>
 
 <p>Finding the largest number.</p>
 <p id="demo"></p>
 
 <script>
 function findMax() {
 var i, max = 0;   //   console.log(arguments);
 for(i = 0; i < arguments[0].argArr.length; i++) {
 if (arguments[0].argArr[i] > max) { max = arguments[0].argArr[i]; }
 }
 return max;
 } 
 document.getElementById("demo").innerHTML = findMax({argArr: [1,2,3,4]});  // literal array
 
 
 
 var tarr = [1,5,100,5,1];
 document.getElementById("demo").innerHTML += '<p>Maximum: ' + findMax({argArr: tarr});
 
 function avg() {
 var i, sum = 0, cnt = arguments[0].argArr.length;   //   console.log(arguments);
 for(i = 0; i < cnt; i++) { sum += arguments[0].argArr[i]; }
 return sum / cnt;
 
 }
 document.getElementById("demo").innerHTML += '<p>Average: ' + avg({argArr: tarr});
 
 </script>
 
 </body>
 </html>
 [/code]

@Jeff_MottMay 10.2015 — #

args = new Array(1,2,3,4,5);
 max = findMax.apply(null, args);

This use of apply() is also what mrhoo was trying to demonstrate above.

@JMRKERauthorMay 10.2015 — #

args = new Array(1,2,3,4,5);
 max = findMax.apply(null, args);

This use of apply() is also what mrhoo was trying to demonstrate above.[/QUOTE]

You're right.

I was just too confused to see the equivalency.

The function I was looking for to do the reverse actions looks like the .apply()

while the .call() is used for the literal assignment or calling the function directly with literal parameters.

[code=php]
 <!DOCTYPE html>
 <html>
 <body>
 
 <p>Finding the largest number.</p>
 <p id="demo"></p>
 
 <script>
 function findMax(){
 var i, max= 0;
 for(i= 0; i<arguments.length; i++) {
 if (arguments[i]>max) { max = arguments[i]; }
 }
 return max;
 }
 document.getElementById("demo").innerHTML = 'arguments: 1,2,3,4<br>max: '+findMax(1,2,3,4);  // literal arguments
 document.getElementById("demo").innerHTML += '<p>arguments: 1,2,3,4<br>max: '+findMax.call(null,1,2,3,4);  // literal arguments
 
 var x = [1, 123, 500, 115, 44, 88];
 document.getElementById('demo').innerHTML += '<p>array: '+x+'<br>maximum: '+findMax.apply(Array,x);
 
 
 
 var tarr = [1,5,100,5,1];
 function avg() {
 var i, sum = 0, cnt = arguments.length;   //   console.log(arguments);
 for(i = 0; i < cnt; i++) { sum += arguments[i]; }
 return sum / cnt;
 }
 document.getElementById("demo").innerHTML += '<p>array: '+tarr+'<br>Average: ' + avg.apply(Array,tarr);
 
 
 </script>
 
 </body>
 </html> 

 [/code]

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