Is setting var _ = this bad practice in javascript -

i looking through open source code other day , noticed used var _ = this; maintain reference original this. novice in javascript wondering if bad practice?

i have seen , used self = this, that = this, me = this, use of underscore makes code easier read in eyes. since in plugin i'm writing requires it's use often. eyes can focus on variable/function more easily.

now question how feel using _ = this;

here code referring to.

https://github.com/kenwheeler/slick/blob/master/slick/slick.js

the question here if need that.

let's suppose have object call lassing callback.

now variable _ have this:

function person( name ) {   var _ = this;   _.name = name;    _.dog = new dog( "fido" );   _.dog.goeat( function() {      // when dog finished eat      _.gooutwithyourdog( );   } );    ... 

in case can same without use _.

function person( name ) {       this.name = name;        this.dog = new dog( "fido" );       this.dog.goeat( function() {          // when dog finished eat          this.gooutwithyourdog( );       }.bind(this) );        ... 

using bind can wrap function , use inside person object.

you can use closer bind, let callback function have context binded caller, can use person object. os usefull when have use callback events. better of use _ because use if need it.

function person( name ) {       this.name = name;       (function(person){         $( ... ).on( "click", function( e ) {            var value = this.value;            person.dosomestuffwiththevalue( value );         } );       })( );