const arrobj = [
{
"programming language": "JavaScript",
"fileextension": "js"
},
{
"programming language": "TypeScript",
"fileextension": "ts"
},
{
"programming language": "C Plus Plus",
"fileextension": "c++"
}
];
const result = arrobj.map(item => item.fileextension);
console.log(result);
/*
run:
[ 'js', 'ts', 'c++' ]
*/