redeclaration

🚧 施工中

⟩ ⟩ ⟩ redeclaration

🚧

JS is lenient with var, strict with let.

"function redeclaration" behaves like "var redeclaration".

the declaration part is ignored.
the assignment part is applied( even in strict mode)

var redeclaration applied even in strict mode❗️ /

replit：

// 'use strict';    // ⭐ toggle sloppy/strict mode

// ⭐ "redeclarations": (2)
// ------------------------------
// • assignments are always applied. 
//   (in both sloppy/strict mode)

// ⭐ "function in block": (3)(4)
// ------------------------------
// • sloppy mode:
//   • is visible outside the block.
//   • can be considered a "redeclaration".
//   • but the assignment is not applied until the block is run❗
//     ((3) is NOT run, (4) is run.)
//
// • strict mode:
//   • is "local" to the block.
//   • never is a "redeclaration".

// ⭐ "if-false-block"
if (false) {
    // (3)
    // -------------------------------
    // • sloppy mode:
    //   "redeclaration" NEVER happens. (because it never runs)
    // • strict mode:
    //   "function in block" is local to the block,
    //   it never is a "redeclaration".
    function foo() { return 3 }            // this line never runs❗
}

// ⭐ "if-true-block"
if (true) {
    // (4)
    // ---------------------------------
    // • sloppy mode:
    //   "redeclaration" DOES happen. (because it runs)
    // • strict mode:
    //   "function in block" is local to the block,
    //   it never is a "redeclaration".
    function foo() { return 4 }            // this line always runs❗
}

// (1)
// ⭐️ function declaration
// -------------------------
function foo() { return 1 }

// (2)
// ❗ function re-declaration
// ---------------------------
// • declaration: ignored
// • assignment : applied❗
function foo() { return 2 }

// log
console.log(foo());        // • sloppy: 4 ❗
                           // • strict: 2 ❗

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Last updated 2 years ago

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// 'use strict'; // ⭐ toggle sloppy/strict mode // ⭐ "redeclarations": (2) // ------------------------------ // • assignments are always applied. // (in both sloppy/strict mode) // ⭐ "function in block": (3)(4) // ------------------------------ // • sloppy mode: // • is visible outside the block. // • can be considered a "redeclaration". // • but the assignment is not applied until the block is run❗ // ((3) is NOT run, (4) is run.) // // • strict mode: // • is "local" to the block. // • never is a "redeclaration". // ⭐ "if-false-block" if (false) { // (3) // ------------------------------- // • sloppy mode: // "redeclaration" NEVER happens. (because it never runs) // • strict mode: // "function in block" is local to the block, // it never is a "redeclaration". function foo() { return 3 } // this line never runs❗ } // ⭐ "if-true-block" if (true) { // (4) // --------------------------------- // • sloppy mode: // "redeclaration" DOES happen. (because it runs) // • strict mode: // "function in block" is local to the block, // it never is a "redeclaration". function foo() { return 4 } // this line always runs❗ } // (1) // ⭐️ function declaration // ------------------------- function foo() { return 1 } // (2) // ❗ function re-declaration // --------------------------- // • declaration: ignored // • assignment : applied❗ function foo() { return 2 } // log console.log(foo()); // • sloppy: 4 ❗ // • strict: 2 ❗