何かわからないグーグルチャート

function init() {
var options = {
width: 400,
height: 240,
animation:{
duration: 1000,
easing: 'out',
},
vAxis: {minValue:0, maxValue:1000}
};
var data = new google.visualization.DataTable();
data.addColumn('string', 'N');
data.addColumn('number', 'Value');
data.addRow(['V', 200]);

var chart = new google.visualization.ColumnChart(
document.getElementById('visualization'));
var button = document.getElementById('b1');

function drawChart() {
// Disabling the button while the chart is drawing.
button.disabled = true;
google.visualization.events.addListener(chart, 'ready',
function() {
button.disabled = false;
});
chart.draw(data, options);
}

button.onclick = function() {
var newValue = 1000 - data.getValue(0, 1);
data.setValue(0, 1, newValue);
drawChart();
}
drawChart();
}