How to keep the value of this when using async.apply? [duplicate]

From your question, this is the model.

then you should change code to

var model = this;var verify = function(reply) {  model.verifyParent(reply);};async.parallel([  async.apply(content, {slug: slug}),  async.apply(verify, req.body.reply),], (err, result) => {      //results});

Because this keyword is context based. See Function context for more.

You can just bind the function to current context like this,

async.parallel([      async.apply(content, {slug: slug}),      async.apply(this.verifyParent.bind(this), req.body.reply),    ], (err, result) => {          //results});

This is the function definition of async.apply, which seems like it calls the passed function with passed arguments, that's why this gets set to parent scope which is express app.

So basically what is happening is this,

function apply(fn) {  return fn();}var model = {  prop: "world",  verifyParent: function () {    console.log("hello", this.prop)  }}// model context is lost.apply(model.verifyParent)// bind to model explicitly.apply(model.verifyParent.bind(model))