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string.replace

alzami

By alzami
in JavaScript

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alzami Newbie

alzami

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Posted

why the first one works and second one doesn't work?

<!doctype html><html><head><meta charset="utf-8"><title>Untitled Document</title><style>#gap{	width:200px;	height:50px;	border:1px solid black;}</style></head><body><div id="gap"></div><p id="thiss">3*x2+4*x2</p><input type="button" value="replace this" onClick="change();"><script>function change(){	var m=document.getElementById("gap");	var n=document.getElementById("thiss").innerHTML;		var rep=n.replace(/x2/g,"Math.pow(3,2)");	m.innerHTML=rep;	var t=eval(m.innerHTML);	m.innerHTML=t;}</script></body></html>

this doesn't work. i used a ( ^ ) sign after x to clearly indicate that it is a square

<!doctype html><html><head><meta charset="utf-8"><title>Untitled Document</title><style>#gap{	width:200px;	height:50px;	border:1px solid black;}</style></head><body><div id="gap"></div><p id="thiss">3*x^2+4*x^2</p><input type="button" value="replace this" onClick="change();"><script>function change(){	var m=document.getElementById("gap");	var n=document.getElementById("thiss").innerHTML;		var rep=n.replace(/x^2/g,"Math.pow(3,2)");	m.innerHTML=rep;	var t=eval(m.innerHTML);	m.innerHTML=t;}</script></body></html>
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Hadien Member

Hadien

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Posted

"^" is a reserved character in regEx, try escaping it first as /x/^2/g

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justsomeguy w3schools Guru

justsomeguy

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Are you suggesting that the eval function in Javascript is broken? If you pass eval a valid string of code, it's going to execute that code. Unless your browser has a non-working eval for some reason. I suggest that you verify that what you are sending to eval is valid code, and check for Javascript errors. Why do you write a value to an element's innerHTML, and then try to eval the innerHTML, instead of just using eval on the value directly? What if the browser changes the value when it goes into innerHTML?

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alzami Newbie

alzami

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Posted (edited)

i am not suggesting anything.i wanted to use a ^ sign to make the statement more understandable.and i am using the string.replace function for the first time.it worked

if i just use x2 instead of x^2.

i used a backslash to seperate ^ as suggested.it shows the replaced string in the text field .not evaluating.

of course there is a mistake.i am failing to figure it out.

this simple code works fine

<!doctype html><html><head><meta charset="utf-8"><title>Untitled Document</title><style>#gap{	width:200px;	height:50px;	border:1px solid black;}</style></head><body><div id="gap"></div><p id="thiss">3*x3</p><input type="button" value="replace this" onClick="change();"><script>function change(){	var m=document.getElementById("gap");	var n=document.getElementById("thiss").innerHTML;	var rep1=n.replace(/x3/g,"3");		m.innerHTML=rep1	var t=eval(m.innerHTML);	m.innerHTML=t;}</script></body></html>

if i pass Math.pow(3,3) in stead of 3 eval function don't evaluate it.It pulish 3*Math.pow(3,3)in the screen.

 

but this script works fine....but what could be the mistakes in previous code?

<script>function change(){	var m=document.getElementById("gap");	var n=document.getElementById("thiss").innerHTML;	var rep1=eval(n.replace(/x3/g,"Math.pow(3,3)"));	m.innerHTML=rep1;}</script>
Edited by alzami
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Hadien Member

Hadien

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you don't need eval, eval is pretty bad anyway. instead of writing 

n.replace(/x3/g,"Math.pow(3,3)")

simply write it as:

n.replace(/x3/g,""+Math.pow(3,3))

the power function will run (best of all only once) and calculate 3^3 and then cast it into a string as "27". then it will run the replace of "27" and not "Math.pow(3,3)".

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justsomeguy w3schools Guru

justsomeguy

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Posted

Why are you doing this:

 

m.innerHTML=rep1

var t=eval(m.innerHTML);

m.innerHTML=t;

 

instead of this:

 

var t=eval(rep1);

m.innerHTML=t;

 

or this:

 

m.innerHTML = eval(rep1);

 

What if the browser transforms the text when you write it to innerHTML? That's what I was talking about earlier, why are you trying to use Javascript to eval innerHTML when eval is supposed to be used on Javascript code? If you run this it works perfectly fine:

 

eval("3*Math.pow(3,3)")

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