php - How do I change the value of a text field on click? -

i making calculator in php. 1 problem have been having trouble with, this.

<input type="button" name="insert" value="0" style="width: 30px; height: 35px" onclick="zerocheck()"> 

so having textfield containing "0", replace 0 instead of adding "0" onto that.

my textfield name called entry.

i tried develop function in order solve problem no avail.

function zerocheck(){     if (entry.value == '0'){         entry.value=='0';     } else{         return entry.value+='0';     } } 

this isn't doing @ all. doing wrong here?

if appreciated.

the simplest solution can think of is:

function zerocheck(el) {     // caching value because it's used multiple times     var v = el.value;     /* setting value ternary/conditional operator:        v == '0' : testing value equal given string        if equal: value set to: '' + v (so there's no change),        if not equal: value set to: '0' + v (so 0 prepended).     */     el.value = ( v == '0' ? '' : '0' ) + v; } 

js fiddle demo.

in linked demo above javascript used following html:

<input type="button" name="insert" value="0" onclick="zerocheck(this)" /> <input type="button" name="insert" value="1" onclick="zerocheck(this)" /> <input type="button" name="insert" value="2" onclick="zerocheck(this)" /> <input type="button" name="insert" value="3" onclick="zerocheck(this)" /> 

to add (basic) error-handling:

function zerocheck(el) {     // caching value, because we're using few times     var v = el.value,     // saving number (this way 1.4 , 1 both preserved)         num = parsefloat(v);      // basic check see value number     // (or rather 'not not-a-number):     if (!isnan(num)) {         el.value = ( v == '0' ? '' : '0' ) + v;     }     else {         // default handling here, handle non-numeric values:         el.value = 0;     } } 

js fiddle demo.

because think mis-read question, i've updated answer possibility, handles sibling text-input elements , takes account values have leading-zero:

function zerocheck(el) {     /* gets 'input' elements within same parentnode        contains button that's clicked: */     var inputs = el.parentnode.getelementsbytagname('input'),     /* declaring variables used in loop, they're not        being re-declared through loop */         v, num;     (var = 0, len = inputs.length; < len; i++) {         v = inputs[i].value;         num = parsefloat(v);          // if input button, don't anything, keep going         if (inputs[i] == el) {             continue;         // otherwise if number not not-a-number:         } else if (!isnan(num)) {             inputs[i].value = (v.charat(0) == '0' ? '' : '0') + v;         } else {             inputs[i].value = 0; // error-handling         }     } } 

js fiddle demo.