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時事ネタ

次回はGW終了直後ですね

-> 普通にGW終了直後にやります

自己紹介 (近況報告)

Go / TSを書いて暮らしてます

また別チャンネルでライブしました

Findyさんのイベントで話しました

色々詰め込み過ぎた感があるのでしばらく休暇したい

首を痛めた

iwatsurut

とくに、イベントもなく過ごしています。

本の数式を写経するだけなら、VSCode の html preview が便利そう

GoとReact

最近はScrapboxのuserscriptを書くのが楽しい

書いたことで満足してあんまり使わないというカスタマイズ沼

突然の数式

$ i\hbar\frac{\partial}{\partial t}\psi(x,t)=\left(-\frac{\hbar^2}{2m}+V(x)\right)\psi(x,t)

Go と Perl

社内でGoのProposal読む会をしたり、OOC2024 staff やったり

前回のあらすじ

1から読んでみる

10. VarScopedDeclarations

難解。あとで要確認

今回の範囲

step16

a. NOTE: Arrow functions never have an arguments object.

code:js

const f = function () {

console.log(arguments);

};

const arrowF = () => {

console.log(arguments);

};

f(1, 2, 3); // 期待通りのargumentsが出る

arrowF(1, 2, 3); // Node.jsの実行コンテキストのargumentsが出てそう

/*

'0': {},

main: {

id: '.',

path: '/Users/syumai/go/src/github.com/syumai/til/js/esspec56',

exports: {},

filename: '/Users/syumai/go/src/github.com/syumai/til/js/esspec56/step16.js',

loaded: false,

children: [],

},

*/

step17

code:js

const f = function (arguments) {

console.log(arguments);

};

const arrowF = (arguments) => {

console.log(arguments);

};

f(1, 2, 3);

arrowF(1, 2, 3);

/*

1

1

*/

step18

code:js

// hasParameterExpressions: true

function f1(a = 1) {}

f1();

// hasParameterExpressions: true

console.log(myA);

}

f2({ a: 1, b: 2 });

/*

18. Else if hasParameterExpressions is false, then

a. If functionNames contains "arguments" or lexicalNames contains "arguments", then

i. Set argumentsObjectNeeded to false.

*/

// hasParameterExpressions: false

function f3() {}

// hasParameterExpressions: false

function f4(a, b) {}

// hasParameterExpressions: false

function f5({ a }) {}

// hasParameterExpressions: false, argumentsObjectNeeded: false

function f6() {

console.log(arguments);

function arguments() {} // functionNames

}

f6();

// hasParameterExpressions: false, argumentsObjectNeeded: false

function f7() {

let arguments = 0; // lexicalNames

console.log(arguments);

}

f7();

// おまけ

function f1() {

var arguments = 1;

console.log(arguments);

}

function f2() {

console.log(arguments);

var arguments = 1;

}

f1(100); // 1

step20

code:js

// 19. If strict is true or hasParameterExpressions is false, the

// 20. Else,

// a. NOTE: A separate Environment Record is needed to ensure that bindings created by direct eval calls in the formal parameter list are outside the environment where parameters are declared.

//

var b = 2;

function f(a = eval("var b = 1"), x = b, y = eval("b = 3")) {

console.log("inside", b, x, y); // 3, 1, 3

}

f();

// console.log("outside", b); // Reference Error

code:js

// 19. If strict is true or hasParameterExpressions is false, the

// 20. Else,

// a. NOTE: A separate Environment Record is needed to ensure that bindings created by direct eval calls in the formal parameter list are outside the environment where parameters are declared.

//

// indirect eval

const _eval = eval;

function f(a = _eval("var b = 1"), x = b, y = _eval("b = 3")) {

console.log("inside", b, x, y); // 3, 1, 3

}

f();

console.log("outside", b); // 3

// step 20のenvironment record差し替えの擬似コード

const outerEnv = {};

const calleeContext = {

VariableEnvironment: outerEnv,

LexicalEnvironment: outerEnv,

};

const env = new DeclarativeEnvironment(outerEnv);

calleeContext.LexicalEnvironment = env;

step21

NOTE: Early errors ensure that duplicate parameter names can only occur in non-strict functions that do not have parameter default values or rest parameters.

code:duplicate parameter namesがSyntaxErrorになる場合とならない場合.js

// OK

function f1(a, a) {

console.log(a);

}

f1(1, 2); // 2

// SyntaxError: Duplicate parameter name not allowed in this context

function f2(a, a, b = 1) {

console.log(a);

}

// SyntaxError: Duplicate parameter name not allowed in this context

function f3(a, a, ...args) {

console.log(a);

}

/*

21. For each String paramName of parameterNames, do

a. Let alreadyDeclared be ! env.HasBinding(paramName).

b. NOTE: Early errors ensure that duplicate parameter names can only occur in non-strict functions that do not have parameter default values or rest parameters.

c. If alreadyDeclared is false, then

i. Perform ! env.CreateMutableBinding(paramName, false).

ii. If hasDuplicates is true, then

1. Perform ! env.InitializeBinding(paramName, undefined).

*/

function f(a, a, b, c) {}

code:_

Let alreadyDeclared be ! env.HasBinding(paramName).

step 22

CreateUnmappedArgumentsObject とは?

CreateMappedArgumentsObject

code:arguments.calleeの例.js

(function () {

console.log(i);

if (i > 10) {

return;

} else {

arguments.callee(i + 1);

}

})(1);

/*

1

2

3

4

5

6

7

8

9

10

11

*/

code:argumentsが再代入できる場合、できない場合.js

/*

22. If argumentsObjectNeeded is true, then

a. If strict is true or simpleParameterList is false, then

i. Let ao be CreateUnmappedArgumentsObject(argumentsList).

b. Else,

i. NOTE: A mapped argument object is only provided for non-strict functions that don't have a rest parameter, any parameter default value initializers, or any destructured parameters.

ii. Let ao be CreateMappedArgumentsObject(func, formals, argumentsList, env).

c. If strict is true, then

i. Perform ! env.CreateImmutableBinding("arguments", false).

ii. NOTE: In strict mode code early errors prevent attempting to assign to this binding, so its mutability is not observable.

d. Else,

i. Perform ! env.CreateMutableBinding("arguments", false).

e. Perform ! env.InitializeBinding("arguments", ao).

f. Let parameterBindings be the list-concatenation of parameterNames and « "arguments" ».

*/

// strict: true

function f1() {

"use strict";

// console.log(arguments.callee); // TypeError

// arguments = {}; // SyntaxError

}

f1(1, 2, 3);

// simpleParameterList: false

function f2(x = 1) {

// console.log(arguments.callee); // TypeError

arguments = {}; // 再代入できる

}

f2(1, 2, 3);

// strict: false && simpleParameterList: true

function f3() {

console.log(arguments.callee); // f3

arguments = {}; // 再代入できる

}

f3(1, 2, 3);

« 1, 2, 3 »

「1, 2, 3の値を持つList」を意味する

このListはECMAScript Specification typesのList type