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<len;i++){
array.push({"projectname":arr[i][0],"projectnumber":arr[i][1]});
}
return JSON.stringify(array);
}