JSFiddle - React, Tailwind, and code Playground

HTML

<input id="date" type="text" name="date" value="２０１６／６／２２">
<button id="convert">
convert
</button>
<div id="result"></div>

JavaScript

// 半角変換 
function numToLower(target) { 
// 全角数字配列 
var fullNumber = new Array("１","２","３","４","５","６","７","８","９","０","／"); 
// 半角数字配列 
var halfNumber = new Array(1,2,3,4,5,6,7,8,9,0,"/"); 
var count; 
while(target.match(/[０-９／]/)){ 
for(count = 0; count < fullNumber.length; count++){ 
target = target.replace(fullNumber[count], halfNumber[count]); 
} 
} 
return target; 
}
$("#convert").on("click", function(e){
$("#result").empty().append(numToLower($("#date").val()));
});