[Vlasenko Fedor]

<input type="text" value="" id="test">
<script>
test.oninput = test.onkeyup = inputFloat;
function inputFloat() {
    this.value = this.value.replace(',', '.');
    if (!/^-?\.?$/.test(this.value)  &&  !isFinite(this.value)) {
        this.value = parseFloat(this.value) || this.value.slice(0, -1);
    }
}
</script>