I want to prevent 0 as the first character. But when I focusout and focusin again, then I add "2" in the first, it still run, I want should not run.
Here is my HTML
<input type="number" id="test"> My JS
$('#test').keypress(function(evt) { if (evt.which == "0".charCodeAt(0) && $(this).val().trim() == "") { return false; } }); Anybody help or suggest what should I do? Thank you.
You can use input event, which also handles pasted values, String.prototype.replace() with RegExp /^0/ to replace all 0 characters found within .value of element
$("#test").on("input", function() { if (/^0/.test(this.value)) { this.value = this.value.replace(/^0/, "") } })<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"> </script> <input type="number" id="test">
^ to beginning of RegExp; initially interpreted requirement for no 0 characters to be able to be entered. Question does not appear to indicate only first character that is 0 should not be allowed?^ to RegExp
+ after 0 in case multiple zeroes are pasted, like so this.value = this.value.replace(/^0+/, "")Compare which property with the ASCII code of number 0 and return false.
if (evt.which === 48) { return false; } 
"0".charCodeAt(0) check?$('#test').on("keypress",function (evt) { if (this.value.length == 1 && evt.which == 48 ) { evt.preventDefault(); } }); 
Try
if (event.target.value.length == 0 && event.which == 48) { return false; } You can simply add condition for this block "0" from first character using --> event.target.value. Here is the following code for block "0" from first character.
Javascript.
const handleOnchange =()=>{ if(event.target.name === "myEvent"){ event.target.value === event.targe.value.replace(/^0/, ""); } } HTML.
<input type="number" name="myEvent" id="myEvent" onChange={handleOnchange} /> 
"0"? (So"02"would not be allowed but"20"would be allowed?) Because if so you can't do that by testing just the current keypress because the user may type the"2"then move the cursor in front of it and type the"0". (Also they may edit the field without using the keyboard, i.e., by pasting or drag'n'drop.)