javascript - Updating function level variable in a fetch request -

i new fetch , react.js , javascript, trying create new row in table , id (second then), problem temp in domain changing not changing outside although defined function level variable

handleaddrow({ newrowindex }) {         var temp = null;          /////////////////////////////////////// updating records in db         fetch(`${config.serverurl}/criteriaapi`,         {             method: "post",             datatype: 'json',             headers: {                     'accept': 'application/json; charset=utf-8',                     'content-type': 'application/json; charset=utf-8'                 }         })         .then(function(res){ return res.json(); })         .then(function(data){  temp = data._id ;alert(temp)})         //////////////////////////////////////         console.log(temp);         const newrow = {             _id: temp,             criteria_id: '',             securitycriteria: '',             description: '',         };        let rows = this.state.rows.slice();         rows = update(rows, {$push: [newrow]});     },    console.log(temp) = > null alert(temp) = > id key : id value 

it looks problem calling console.log(temp) without waiting previous promises complete, execution has not yet come point assign value temp variable. value of temp variable change - happens time after console.log(temp) gets executed.

if want use temp variable , filled in asynchronous manner - must access in corresponding then handlers.