Unable to use array.includes() with SSJS?

i have the following functions i’m using to not only collect all DEs in an account but using the JSON payload from that, also extract all the Business Unit IDs.

Within the pullAllBusinessUnits() function below, i have a simple if statement, basically if the Business Unit ID doesn’t exist in the allBusinessUnits[] then add it.

 function pullAllDataExtensions() {
    var prox                            = new Script.Util.WSProxy();
    var moreData                        = true;
    var reqID                           = null;
    var cols                            = ["Name","CustomerKey","CategoryID","IsSendable", "Client.ID"];
    var filterAllDataExtensions         = {
                                            LeftOperand: {
                                                Property        : "IsSendable",
                                                SimpleOperator  : "equals",
                                                Value           : true
                                            },
                                            LogicalOperator: "OR",
                                            RightOperand: {
                                                Property        : "IsSendable",
                                                SimpleOperator  : "equals",
                                                Value           : false
                                            }
                                        }
    var options                         = {IncludeObjects: true};
    var props                           = {   
        QueryAllAccounts: true
    };
    var dataExtensionResults            = [];
    while(moreData) {
        moreData = false;
        var data = reqID == null ?
            prox.retrieve("DataExtension", cols, filterAllDataExtensions, options, props) : 
            prox.getNextBatch("DataExtension", reqID);
        if(data != null) {
            moreData    = data.HasMoreRows;
            reqID       = data.RequestID;
            if (data && data.Results) {
                for (i=0; i < data.Results.length; i++) {
                    dataExtensionResults.push(data.Results[i])
                }
            }
        }
        
        if (debug == true) {
            Write("Results: " + data.Results.length)
            Write(Stringify(data))
        }
    };
    return dataExtensionResults
}

// Write(Stringify(pullAllDataExtensions()))

function pullAllBusinessUnits() {
    var allDataExtensions = pullAllDataExtensions();
    var allBusinessUnits = [];

    for (i=0; i < allDataExtensions.length; i++) {
        var buID = allDataExtensions[i].Client.ID

        if (!allBusinessUnits.includes(buID)){
            allBusinessUnits.push(allDataExtensions[i].Client.ID)
        } 
    };

    return allBusinessUnits
}

Write(Stringify(pullAllBusinessUnits())) // using for debug 

My issue? For some reason, the response i get when i use the array.includes() method is that it is expecting an object – see below. Anyone know why this is and how i can possibly fix the code?

{"message":"Object expected: includes","jintException":"Jint.Native.JsException: Exception of type 'Jint.Native.JsException' was thrown.rn at Jint.ExecutionVisitor.Visit(MethodCall methodCall)rn at Jint.Expressions.MethodCall.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(MemberExpression expression)rn at Jint.Expressions.MemberExpression.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(UnaryExpression expression)rn at Jint.Expressions.UnaryExpression.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(IfStatement statement)rn at Jint.Expressions.IfStatement.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(BlockStatement statement)rn at Jint.Expressions.BlockStatement.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(ForStatement statement)rn at Jint.Expressions.ForStatement.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(BlockStatement statement)rn at Jint.Expressions.BlockStatement.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.CallFunction(JsFunction function, JsDictionaryObject that, JsInstance[] parameters)rn at Jint.Native.JsFunction.Execute(ExecutionVisitor visitor, JsDictionaryObject that, JsInstance[] parameters)rn at Jint.ExecutionVisitor.ExecuteFunction(JsFunction function, JsDictionaryObject that, JsInstance[] parameters)rn at Jint.ExecutionVisitor.Visit(MethodCall methodCall)rn at Jint.Expressions.MethodCall.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(MemberExpression expression)rn at Jint.Expressions.MemberExpression.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(MethodCall methodCall)rn at Jint.Expressions.MethodCall.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(MemberExpression expression)rn at Jint.Expressions.MemberExpression.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(MethodCall methodCall)rn at Jint.Expressions.MethodCall.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(MemberExpression expression)rn at Jint.Expressions.MemberExpression.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(ExpressionStatement statement)rn at Jint.Expressions.ExpressionStatement.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(BlockStatement statement)rn at Jint.Expressions.BlockStatement.Accept(IJintVisitor visitor)rn at Jint.ExecutionVisitor.Visit(TryStatement statement)","description":"Jint.Native.JsException: Object expected: includesrnException of type 'Jint.Native.JsException' was thrown. - from Jintrnrn"}