How can I limit possible inputs in a HTML5 “number” element?

Question

For element, maxlength is not working. How can I restrict the maxlength for that number element?

Answer 1

As I found out you cannot use any of onkeydown, onkeypress or onkeyup events for a complete solution including mobile browsers. By the way onkeypress is deprecated and not present anymore in chrome/opera for android (see: UI Events W3C Working Draft, 04 August 2016).

I figured out a solution using the oninput event only. You may have to do additional number checking as required such as negative/positive sign or decimal and thousand separators and the like but as a start the following should suffice:

function checkMaxLength(event) {
	// Prepare to restore the previous value.
	if (this.oldValue === undefined) {
		this.oldValue = this.defaultValue;
	}

	if (this.value.length > this.maxLength) {
		// Set back to the previous value.
		this.value = oldVal;
	}
	else {
		// Store the previous value.
		this.oldValue = this.value;
		
		// Make additional checks for +/- or ./, etc.
		// Also consider to combine 'maxlength'
		// with 'min' and 'max' to prevent wrong submits.
	}
}

I would also recommend to combine maxlength with min and max to prevent wrong submits as stated above several times.