open_form.js

function openEntityForm() {
    var entityFormOptions = {
        entityName: "account",
        useQuickCreateForm: false
    };

    var formParameters = {
        name: "Sample Account",
        description: "This is example of how you can prepopulate the fields on opened entity"
    };

    Xrm.Navigation.openForm(entityFormOptions, formParameters).then(
        success => {
            console.log(success);
        },
        error => {
            console.log(error);
        });
}