javascript - Cannot setState inside callback -


following code used set state.

handleaddnewquiz(event){     this.quiz = new quiz(this.db, this.newquizname, function(err, affected, value){         if(!err){             this.setstate( { quiz : value});  // error: cannot read property 'setstate' of undefined         }     });     event.preventdefault(); };

rven though database created successfully, cannot call this.state, it's undefined.

i tried:

self = this;  handleaddnewquiz(event){     this.quiz = new quiz(this.db, this.newquizname, function(err, affected, value){         if(!err){             self.setstate( { quiz : value});  // error: self.setstate not function         }     });     event.preventdefault(); };

but still fails, tried a = this, , use a.setstate, still no luck.

how can solve this?

use arrow function bind context, use this:

 handleaddnewquiz(event){         this.quiz = new quiz(this.db, this.newquizname, (err, affected, value) => {             if(!err){                 this.setstate( { quiz : value});              }         });         event.preventdefault();     };

or use .bind(this) callback method, this:

handleaddnewquiz(event){     this.quiz = new quiz(this.db, this.newquizname, function(err, affected, value){         if(!err){             this.setstate( { quiz : value});           }     }.bind(this));     event.preventdefault(); };

the way using work, save reference of this inside handleaddnewquiz method, way:

handleaddnewquiz(event){     let self = this;    //here save reference of     this.quiz = new quiz(this.db, this.newquizname, function(err, affected, value){         if(!err){             self.setstate( { quiz : value});           }     });     event.preventdefault(); };

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