Working with functions

[dx27s]

I want a function to take another function as a parameter, and execute
it as a line of code. I put a simplified example below, just to
illustrate the idea. Does anyone know the syntax to do this, or is there
perhaps a better approach entirely?

// EXAMPLE

doSomething(5, 10, functionA, functionB);

function doSomething(x, y, myFunctionA, myFunctionB) {
if (x > y) {
myFunctionA();
} else {
myFunctionB();
}
}

function functionA() {
// some code
}

function functionB() {
// some code
}

[jdlwright]

I suspect there is a better approach, but without knowing what your
underlying intention is it's hard to say... but you should look at the
eval function which will do what you want.

Jim

[web.dev]

dx27s wrote:

I want a function to take another function as a parameter, and execute
it as a line of code. I put a simplified example below, just to
illustrate the idea. Does anyone know the syntax to do this, or is there
perhaps a better approach entirely?

// EXAMPLE

doSomething(5, 10, functionA, functionB);

function doSomething(x, y, myFunctionA, myFunctionB) {
if (x > y) {
myFunctionA();
} else {
myFunctionB();
}
}

function functionA() {
// some code
}

function functionB() {
// some code
}

:) did you know you already got the solution? That is the correct
syntax for passing a function reference to another function.

[Randy Webb]

dx27s said the following on 10/25/2005 3:52 PM:

I want a function to take another function as a parameter, and execute
it as a line of code. I put a simplified example below, just to
illustrate the idea. Does anyone know the syntax to do this, or is there
perhaps a better approach entirely?

// EXAMPLE

doSomething(5, 10, functionA, functionB);

function doSomething(x, y, myFunctionA, myFunctionB) {
if (x > y) {
myFunctionA();

window[myFunctionA]();

--
Randy
comp.lang.javascript FAQ - http://jibbering.com/faq & newsgroup weekly

[Dr John Stockton]

JRS: In article <11**********************@g43g2000cwa.googlegroups .com>
, dated Tue, 25 Oct 2005 13:50:50, seen in news:comp.lang.javascript,
jd*******@gmail.com posted :

I suspect there is a better approach, but without knowing what your
underlying intention is it's hard to say... but you should look at the
eval function which will do what you want.

Jim

Obviously not Our Jim.

A good way to avoid (to some extent) writing complete twaddle is to
first read and understand the newsgroup FAQ.

--
© John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v4.00 IE 4 ©
<URL:http://www.jibbering.com/faq/> JL/RC: FAQ of news:comp.lang.javascript
<URL:http://www.merlyn.demon.co.uk/js-index.htm> jscr maths, dates, sources.
<URL:http://www.merlyn.demon.co.uk/> TP/BP/Delphi/jscr/&c, FAQ items, links.

[jdlwright]

What's wrong with suggesting eval?

He can acheive the same *result* with eval, can he not?

doSomething(5, 10, "functionA", "functionB");
function doSomething(x, y, myFunctionA, myFunctionB) {
if (x > y) {
eval(myFunctionA+"()");
} else {
eval(myFunctionB+"()") }

}
function functionA() {
// some code
}
function functionB() {
// some code
My understanding was that this group was for *helping*, I didnt realise
we were comissioned to provide 100% accurate and knowledgable answers.
My advice, to see the eval function would have lead him to a reasonable
solution.

"Twaddle", POPPYCOCK!!

Jim

[Randy Webb]

jd*******@gmail.com said the following on 10/26/2005 2:12 PM:

Please quote what you are replying to.

If you want to post a followup via groups.google.com, don't use the
"Reply" link at the bottom of the article. Click on "show options" at
the top of the article, then click on the "Reply" at the bottom of the
article headers.

What's wrong with suggesting eval?
You mean other than the fact it isn't needed, makes the code slower
(albeit minimally) and there is a better alternative?
He can acheive the same *result* with eval, can he not?
No. But to understand that answer you have to understand eval itself.
doSomething(5, 10, "functionA", "functionB");
function doSomething(x, y, myFunctionA, myFunctionB) {
if (x > y) {
eval(myFunctionA+"()");
} else {
eval(myFunctionB+"()") }
}
function functionA() {
// some code
}
function functionB() {
// some code
My understanding was that this group was for *helping*, I didnt realise
we were comissioned to provide 100% accurate and knowledgable answers.
This newsgroup is for the "discussion of javascript" and has been
extended to cover JScript and ECMAScript. It is not a "help desk". If
you get an answer to your question - great. If not, you keep going. This
is NOT a help desk.
My advice, to see the eval function would have lead him to a reasonable
solution.

No, it would have lead him to using something that was not optimal nor
designed for that purpose. Did you see/try/test my solution? It doesn't
use eval.

--
Randy
comp.lang.javascript FAQ - http://jibbering.com/faq & newsgroup weekly

[jdlwright]

Randy Webb wrote:

jd*******@gmail.com said the following on 10/26/2005 2:12 PM:

Please quote what you are replying to.

If you want to post a followup via groups.google.com, don't use the
"Reply" link at the bottom of the article. Click on "show options" at
the top of the article, then click on the "Reply" at the bottom of the
article headers.

Sorry Randy, if I had done that it would have been obvious that I was
replying to the honourable Doctor, who shot down my suggestion and told
me to read the FAQ.

Your answer was more ideal, and I did note in my reply (which was
first) that there probably were better ways to do it.

Just trying to help out, but getting shot down is really annoying -
your suggestion was spot on, and I had no intention of arguing with you
- I really just wanted to know what issue the Doctor had with my
answer.

Sorry and thanks

Jim

[Randy Webb]

jd*******@gmail.com said the following on 10/26/2005 2:25 PM:

Randy Webb wrote:

jd*******@gmail.com said the following on 10/26/2005 2:12 PM:

Please quote what you are replying to.

If you want to post a followup via groups.google.com, don't use the
"Reply" link at the bottom of the article. Click on "show options" at
the top of the article, then click on the "Reply" at the bottom of the
article headers.
Sorry Randy, if I had done that it would have been obvious that I was
replying to the honourable Doctor, who shot down my suggestion and told
me to read the FAQ.

I am not sure my opinion of him is the same as yours.
Just trying to help out, but getting shot down is really annoying -
your suggestion was spot on, and I had no intention of arguing with you
- I really just wanted to know what issue the Doctor had with my
answer.

That's typical of John. After a while you learn to cope with him. As for
getting shot down, if I had a US Dollar for every time I have been shot
down in this group I would retire to the Bahamas somewhere. Don't let it
discourage you, take it as a learning process.

--
Randy
comp.lang.javascript FAQ - http://jibbering.com/faq & newsgroup weekly

[Lasse Reichstein Nielsen]

dx27s <dx***@yahoo.com> writes:

I want a function to take another function as a parameter, and execute
it as a line of code. I put a simplified example below, just to
illustrate the idea. Does anyone know the syntax to do this, or is
there perhaps a better approach entirely?

You got it. That's exactly how I would do it too.

In Javascript, functions are first class values, and can be
passed as arguments to other functions (or themselves, even :)

There is no need to pass around the names of functions, it just
means that you have to do an extra lookup later. And don't
use "eval" for resolving names, even if you do pass them around.
It's too fragile compared to other ways of doing name resolution.

You can also return a function, so one different approach would
let you return a choice of a function:

---
function selectFunc(x, y, funcA, funcB) {
if (x > y) {
return funcA;
} else {
return funcB;
}
}

function functionA(x) {
document.write(y);
}
function functionB(y) {
alert(x);
}

doSomething(5, 10, functionA, functionB)("Hello world");

---

Or even inline:
---
var x = 5, y=10;
((x > y) ? functionA : functionB)("Hello world");
---

On the other hand, if what you have solves your problem, there is
absolutely nothing wrong with it, and there isn't anything that is
consistently better.

/L
--
Lasse Reichstein Nielsen - lr*@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleDOM.html>
'Faith without judgement merely degrades the spirit divine.'

[Lasse Reichstein Nielsen]

Randy Webb <Hi************@aol.com> writes:

doSomething(5, 10, functionA, functionB);
function doSomething(x, y, myFunctionA, myFunctionB) {
if (x > y) {
myFunctionA();

window[myFunctionA]();

that would require changing the call to:
doSomething(5, 10, "functionA", "functionB");
i.e., passing the name instead of the function itself ... which there
isn't any good reason to do.

/L
--
Lasse Reichstein Nielsen - lr*@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleDOM.html>
'Faith without judgement merely degrades the spirit divine.'

[dx27s]

Lasse Reichstein Nielsen wrote:

dx27s <dx***@yahoo.com> writes:

I want a function to take another function as a parameter, and execute
it as a line of code. I put a simplified example below, just to
illustrate the idea. Does anyone know the syntax to do this, or is
there perhaps a better approach entirely?

You got it. That's exactly how I would do it too.

Thanks to everyone for all the help and insight.

[Dr John Stockton]

JRS: In article <11**********************@g49g2000cwa.googlegroups .com>
, dated Wed, 26 Oct 2005 11:25:55, seen in news:comp.lang.javascript,
jd*******@gmail.com posted :

Randy Webb wrote:

jd*******@gmail.com said the following on 10/26/2005 2:12 PM:

Just trying to help out, but getting shot down is really annoying -
your suggestion was spot on, and I had no intention of arguing with you
- I really just wanted to know what issue the Doctor had with my
answer.

Mainly its pig-headedness.

--
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