Array Object pushing records

If you look at the commented variable var dataSource; I am trying to reproduce this but the code isn't working when logging it doesn't display the second record with the proper values;

//var dataSource = [{ time: 1730, pwr: 546},{ time: 1731, pwr: 705}];

var chartData=[];
var chartRecord={}

chartRecord["time"] = 1730;
chartRecord["pwr"] = 546;

chartData.push(chartRecord);

chartRecord["time"] = 1731;
chartRecord["pwr"] = 745;

chartData.push(chartRecord);

console.log(chartData);

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