JS中的数组转变成JSON格式字符串的方法

var arr = [["projectname1","projectnumber1"],["projectname2","projectnumber2"],["projectname3","projectnumber3"]]; 

var jsOnarr= [{"projectname":projectname1,"projectnumber":projectnumber1},{"projectname":projectname2,"projectnumber":projectnumber2},{"projectname":projectname3,"projectnumber":projectnumber3}]; 

function tojson(arr){ 
  if(!arr.length) return null; 
  var i = 0; 
  len = arr.length, 
  array = []; 
  for(;i