❗modify current scope at runtime❗️

🚧 施工中

JS ⟩ concepts ⟩ scope ⟩ modify current scope at runtime

eval("var a = 'aaa!';");

sloppy mode：

will introduce a new variable into the current scope. (I think "modify scope" is not accurate, "modify lexical environment" maybe❓) 👉 lexical environment vs. scope

strict mode：

will not introduce a new variable into the current scope, the newly created variable is local to the inner script. ( 👉 eval has its own scope in strict mode )

replit：modify scope at runtime

function modifyScope() {
    
    // ⭐️ modify current (function) scope at runtime
    eval("var a = 'aaa!';");
    //        ╰── `a` is in "function scope"❗
    
    console.log(a);    // `a` is visible.
}

modifyScope();                       // aaa!

replit：modify scope at runtime (with)

var scope = { name: "Joy" };

// ⭐️ `with`
// -------------------------------------------------------
// turns an object into a local scope, 
// its properties are treated as identifiers in the block:
with (scope) {
    console.log(name);   // Joy
    //          ^^^^     // `name` is visible.
}

Previousaccidental global variable in sloppy mode❗️Nextstrict vs. sloppy

Last updated 1 year ago