Create a chart and specify labels with Visualization API

visualization_create_label.js

app.visualization.create( 'pivot-table',
    [
        "Year",  //dimension
        {"qDef" : { "qFieldDefs" : ["Case Owner Group"], "qFieldLabels" : ["Group"] }},           //dimension with label
        {"qDef" : { "qDef" : "=Avg([Case Duration Time])", "qLabel" : "Avg Case Duration Time" }},//measure with label
        {"qDef" : { "qDef" : "Sum( [Open Cases] )", "qLabel" : "Open Cases" }}                    //measure with label
    ],
    {"title" : "Case Owner Group Case stats per year"}
).then( function ( visual ) {
    visual.show( 'QV01' );
} );