javascript tome iii - Qqs caractéristiques du mode strict PDF

[PDF] javascript tome iii - Qqs caractéristiques du mode strict

Assigning to Undeclared Variables

Strict mode makes it impossible to accidentally create global variables. In sloppy mode, mistyping a variable in an assignment creates a new property on the global object and continues to "work". Assignments which would accidentally create global variables throw an error in strict mode:

Failing to Assign to Object Properties

Strict mode makes assignments which would otherwise silently fail to throw an exception. There are three ways to fail a property assignment: 1. assignment to a non-writable data property 2. assignment to a getter-only accessor property 3. assignment to a new property on a non-extensibleobject For example, NaN is a non-writable global variable. In s...

Failing to Delete Object Properties

Attempts to delete a non-configurable or otherwise undeletable (e.g. it's intercepted by a proxy's deleteProperty handler which returns false) property throw in strict mode (where before the attempt would have no effect): Strict mode also forbids deleting plain names. delete namein strict mode is a syntax error: If the name is a configurable global...

Duplicate Parameter Names

Strict mode requires that function parameter names be unique. In sloppy mode, the last duplicated argument hides previous identically-named arguments. Those previous arguments remain available through arguments, so they're not completely inaccessible. Still, this hiding makes little sense and is probably undesirable (it might hide a typo, for examp...

Legacy Octal Literals

Strict mode forbids a 0-prefixed octal literal or octal escape sequence. In sloppy mode, a number beginning with a 0, such as 0644, is interpreted as an octal number (0644 === 420), if all digits are smaller than 8. Novice developers sometimes believe a leading-zero prefix has no semantic meaning, so they might use it as an alignment device — but t...

Setting Properties on Primitive Values

Strict mode forbids setting properties on primitive values. Accessing a property on a primitive implicitly creates a wrapper object that's unobservable, so in sloppy mode, setting properties is ignored (no-op). In strict mode, a TypeErroris thrown.

View PDF Document

What does 'use strict' mean in JavaScript?

It is not a statement, but a literal expression, ignored by earlier versions of JavaScript. The purpose of "use strict" is to indicate that the code should be executed in "strict mode". With strict mode, you can not, for example, use undeclared variables. All modern browsers support "use strict" except Internet Explorer 9 and lower:

What happens if a type error is thrown in strict mode?

In strict mode, a TypeError is thrown. Duplicate property names used to be considered a SyntaxError in strict mode. With the introduction of computed property names, making duplication possible at runtime, this restriction was removed in ES2015. Note: Making code that used to error become non-errors is always considered backwards-compatible.

What is the difference between Sloppy mode and strict mode?

Strict mode treats these mistakes as errors so that they're discovered and promptly fixed. Strict mode makes it impossible to accidentally create global variables. In sloppy mode, mistyping a variable in an assignment creates a new property on the global object and continues to "work".

View PDF Document

[PDF] javascript tome iii - Qqs caractéristiques du mode strict

Assigning to Undeclared Variables

Failing to Assign to Object Properties

Failing to Delete Object Properties

Duplicate Parameter Names

Legacy Octal Literals

Setting Properties on Primitive Values

What does 'use strict' mean in JavaScript?

What happens if a type error is thrown in strict mode?

What is the difference between Sloppy mode and strict mode?

RECOMMANDATIONS POUR LA MISE EN ŒUVRE DUN SITE

REAGIR MAINTENANT POUR LIMITER UNE NOUVELLE VAGUE

Exercices corrigés

Surpoids et obésité de ladulte : prise en charge médicale de

Etude des prestations daide et daccompagnement à domicile et

Actualisation des précautions standard

Les théories de la motivation

GUIDE DE BONNES PRATIQUES POUR LA PRÉVENTION DES

HTML et Javascript

Administration des médicaments par voie intraveineuse aux soins