maxlength ignored for input type=”number” in Chrome

From MDN’s documentation for <input>

If the value of the type attribute is text, email, search, password, tel, or url, this attribute specifies the maximum number of characters (in Unicode code points) that the user can enter; for other control types, it is ignored.

So maxlength is ignored on <input type="number"> by design.

Depending on your needs, you can use the min and max attributes as inon suggested in his/her answer (NB: this will only define a constrained range, not the actual character length of the value, though -9999 to 9999 will cover all 0-4 digit numbers), or you can use a regular text input and enforce validation on the field with the new pattern attribute:

<input type="text" pattern="\d*" maxlength="4">