ReferenceError: $ is not defined

Okay, so I have the following:

$(function(){
    $.getJSON(' https://app.knowledgeowl.com/api/head/article.json', {
            _authbykey: "56a7d8c123131c4058361687",
                project_id: "55c4ffd132131c789e294fe6",
            "status[$in][]": "published",
            "status[$in][]": "review",
            "_fields[]": "name"
        }, function(data) {           
            console.log(data);
        }); //get JSON
});

And I kept getting this error:

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