Cache the array length to speed up for loop. Preassign the array length instead of testing it again in every step.

cachelength.js

/* //Below code is causing the slowdown
for (var i = 0; i < records.length; i++) {
    var record = new recordTemplate(records[i]);
    this.store.add(record);
}
},
*/

// Better code
var records2 = [];
var recLength = records.length;
for (var i = 0; i < recLength; i++) {
    records2.push(new recordTemplate(records[i]));
}

this.store.insert(0, records2);