Full code:-

function onSubmit() {
var arr=[];
var loc=g_form.getValue('create_new_sites');// Internal name of multiline variable set
if(loc == '[]' ){
g_form.addErrorMessage('You must enter at least 1 row');
return false;
}
var data = JSON.parse(loc);
var ct= 0;
for(var i in data){
if (data.hasOwnProperty(i)) {
arr.push(data[i].name1.toString().replace(/\s/g, "") ;
}

ct=ct+1;
}

function removeDuplicate(arr) {
var c;
var len = arr.length;
var result = [];
var obj = {};
for (c = 0; c<len; c++) {
obj[arr[c]] = 0;
}
for (c in obj) {
result.push(c);
}
return result;
}
if(removeDuplicate(myArr).length>0){
g_form.addErrorMessage('Duplicate value present');
return false;
}
}