JSFiddle - React, Tailwind, and code Playground

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;
}
console.log(numToLower('０５／０５'));