eval解惑

Posted 2022-03-05 little-ab

let a = 1,
  b = 2,
  c = 3;

let arr = [a, b, c];

function test(p1, p2, p3) 
  console.log(`$p1 ~ $p2 ~ $p3 ~ `);


test(...arr);     //1 ~ 2 ~ 3 ~
eval(`test($arr)`);     //1 ~ 2 ~ 3 ~     这里等价于eval(`test(a,b,c)`)
test(arr);    //1,2,3 ~~~ undefined ~~~ undefined ~~~  
test(arr.toString());    //1,2,3 ~~~ undefined ~~~ undefined ~~~   这个等价于test(‘1,2,3‘)

eval(‘context.fn(‘ + args +‘)‘)    args=[‘arguments[1]‘,‘arguments[2]‘,...]
数组的展开效果与 eval 无关，是隐式类型导致的，我们来看一个例子：
console.log(‘1‘ + [1, 2, 3]) // 11,2,3

 

function fn(name) 
    console.log(‘my name is ‘ + name);


let name = ‘hello‘;

eval(‘fn(‘ + ‘name‘ + ‘)‘);  //my name is hello
eval(‘fn(‘ + name + ‘)‘); //Uncaught ReferenceError: hello is not defined