// 1. add control to map
var map = L.map("map", {
        center: [29, 120],
    });
L.control.measure().addTo(map);

// 2. using action directly
var measureAction = new L.MeasureAction(map, {
    model: "distance", // 'area' or 'distance', default is 'distance'
});
// measureAction.setModel('area');
measureAction.enable();

L.Measure = {
    linearMeasurement: "Distance measurement",
    areaMeasurement: "Area measurement",
    start: "Start",
    meter: "m",
    meterDecimals: 0,
    kilometer: "km",
    kilometerDecimals: 2,
    squareMeter: "m²",
    squareMeterDecimals: 0,
    squareKilometers: "km²",
    squareKilometersDecimals: 2
};