javascript - Why this is referring the outside variable? -

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• how access correct `this` inside callback? 6 answers

this should refer object in following code why it's behaving differently?

var x   = 4,     obj = {         x: 3,         bar: function() {             var x = 2;             settimeout(function() {                 var x = 1;                 alert(this.x);             }, 1000);         }     }; obj.bar(); 

why alert 4 instead of 3?

inside settimeout callback this refers window object, it's retrieving variable defined in global context.

you can make working binding context using function#bind method .

var x = 4,    obj = {      x: 3,      bar: function() {        var x = 2;        settimeout(function() {          var x = 1;          alert(this.x);        }.bind(this), 1000);      }    };  obj.bar();

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or use local variable cache reference this , use inside callback function.

var x = 4,    obj = {      x: 3,      bar: function() {        var x = 2,          = this;        settimeout(function() {          var x = 1;          alert(that.x);        }, 1000);      }    };  obj.bar();

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also refer mdn documentation : the "this" problem