不可变数据结构：ECMA 4 中的记录和元组

// creating an immutable record const kittyfacts =  #{ name: "turbodog", age: 17, favoritetoy: "laser pointer" };  // accessing values  console.log(kittyfacts.name);  // outputs: turbodog  console.log(kittyfacts.favoritetoy);  // outputs: laser pointer  // attempting to modify will create a new instance  const updatedkittyfacts = #{ ...kittyfacts, age: 18 }; console.log(kittyfacts.age);  // outputs: 17 (unchanged)  console.log(updatedkittyfacts.age);  // outputs: 18 (new instance) 

// creating an immutable tuple  const concertsetlist = #[ "tupelo", "live oak", "strawberry woman", "elephant" ];  // accessing values  console.log(concertsetlist[0]);  // outputs: tupelo  console.log(concertsetlist[2]);  // outputs: strawberry woman  // attempting to modify will create a new instance  const updatedsetlist = #[...concertsetlist, "chaos and clothes"];  console.log(concertsetlist.length);   // outputs: 4 (unchanged)  console.log(updatedsetlist.length); // outputs: 5 (new instance) 

// Creating a Tuple  const originalMixtape = #[ "If We Were Vampires", "World Leader Pretend", "Right Back to It" ];  // Updating a specific index  const updatedMixtape = originalMixtape.with(1, "Turn You Inside-Out");  console.log(originalMixtape);  // Outputs: #[ "If We Were Vampires", "World Leader Pretend", "Right Back to It" ];  console.log(updatedMixtape);  // Outputs: #[ "If We Were Vampires", "Turn You Inside-Out", "Right Back to It" ];