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JS eval()
eval()
function , as a String pass किये गए JavaScript code को evaluate करके result return करता है , eval()
function में pass की गयी String को as a script parse / evaluate होती है।
for example
console.log(eval('2 + 2'));
console.log(eval('4 * 5'));
console.log(eval('10 / 5'));
4 20 2
अब हालाँकि आप जानते हैं कि JavaScript में String को कई तरह से define करते हैं तो आप , single quote string की जगह double quotes , back ticks या String function का use भी कर सकते हैं।
console.log(eval("2 + 2"));
console.log(eval( String(`10 % 3`) ));
console.log(eval(`10 / 5`));
4 1 2
ध्यान रहे कि example में String function का use किया गया है String object का नहीं , eval()
function में String object work नहीं करेगा।
console.log(eval( new String("2 + 3") ));
String { "2 + 3" }
normal statements की तरह ही आप eval() function में भी variables को use कर सकते हैं या उन पर कोई calculation कर सकते हैं।
for example
let x = 20;
let y = 10;
console.log(eval( 'x'));
console.log(eval( 'y'));
console.log(eval( 'x*y'));
console.log(eval( 'x-y'));
20 10 200 20
बैसे तो eval()
function में pass किये गए data के according , completion value return
होगी लेकिन अगर evaluation के बाद completion value empty होती है तो undefined
return होगा।
console.log(eval("")); // undefined
eval() method को अभी तक आपने directly string में data pass करके call किया है है , हालाँकि इसे indirectly भी कई तरीके से use किया जा सकता है।
let x = 20, y = 10;
// Indirect call using the comma operator to return eval
console.log((0, eval)("x + y"));
// Indirect call through optional chaining method.
console.log(eval?.("x + y"));
// Indirect call using a variable to store and return eval.
const geval = eval;
console.log(geval("x + y"));
// Indirect call through member access.
const obj = { eval };
console.log(obj.eval("x + y"));
Output
30 30 30 30
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