Manage Allow Multiple Selection in Task List Assigned to Field using JSOM

Implementation:

• Declare the public variables.
• Get Host Web URL and App web URL in Document Ready.
• Then call MakeMultiSelectionToUserField method.
• Get app context site from AddEnterpriseColumnToList method.
• Get web and Task list.
• Get assigned to filed by Internal name.
• Then case to the assigned to field to user field.
• Set Allow multiple values to True.
• Load the user Field.
• Execute the request.
• Show result in success method.
• Failure method are used to catch the errors.

//Varibles Declaration
var appWebURL, hostWebURL, appCtxSite, context;

// This code runs when the DOM is ready and creates a context object which is needed to use the SharePoint object model
$(document).ready(function () {
     hostWebURL = decodeURIComponent(manageQueryStringParameter('SPHostUrl'));
     appWebURL = decodeURIComponent(manageQueryStringParameter('SPAppWebUrl'));
     MakeMultiSelectionToUserField();
});
//Make assigned to field accept multivalues
function MakeMultiSelectionToUserField() {
    hostWebURL = decodeURIComponent(manageQueryStringParameter('SPHostUrl'));
    appWebURL = decodeURIComponent(manageQueryStringParameter('SPAppWebUrl'))
    var context = new SP.ClientContext(appWebURL);
    var appCtxSite = new SP.AppContextSite(context, hostWebURL);
    //get Web
    var web = appCtxSite.get_web();
    //Get list by title
    var list = web.get_lists().getByTitle('Tasks');
    //Get assigned to  by internal name
    var field = list.get_fields().getByInternalNameOrTitle("AssignedTo");
    var userField = context.castTo(field, SP.FieldUser);
   //Manage allow multiple values for assigned to column
    userField.set_allowMultipleValues(true);
    userField.update();
    context.load(userField);
    context.executeQueryAsync(function () {
    //Success Method
        alert(userField.get_allowMultipleValues());
        console.log("Field added successfully!!" + field);
    }
       , function (sender, args) {
//Failure method Method
           console.log("Request failed" + args.get_message());
       });

}

//Getting host web url and app web url from query string using this method
function manageQueryStringParameter(paramToRetrieve) {
    var params = document.URL.split("?")[1].split("&");
    var strParams = "";
    for (var i = 0; i < params.length; i = i + 1) {
        var singleParam = params[i].split("=");
        if (singleParam[0] == paramToRetrieve) {
            return singleParam[1];
        }
    }
}

Summary

In this blog, we have explored how to allow multiple selection users in SharePoint task list assigned to field using JavaScript Object model. I hope above explained solution is very useful to you. Happy Coding!