JavaScript Grievances

JavaScript Grievances

common complaints

about JavaScript

Seinfeld Festivus Airing of Grievances



Copyright ? 2012-2013 by Object Computing, Inc. (OCI).

All rights reserved.

Assessment Key

E - Addressed by EcmaScript 6 (ES6)

D - Doesn¡¯t really happen in practice

L - Caught by Linting tools (JSLint/JSHint) and/or ES5 strict mode

P - Personal preference

R - Real problem

Y - You can easily learn how to deal with this

Copyright ? 2012-2014 by Object Computing, Inc. (OCI).

All rights reserved.

10 - 2

JS Grievances

Crockford¡¯s Bad Parts ...

Implied globals (E, L)

assign to a variable without a var and it becomes global

can¡¯t do in strict mode

in ES6, use let instead of var

Scope (E, Y)

variables are scoped to a function body or they are global

no block scope in things like if statements and loops (see let in ES6)

CoffeeScript and Node.js provide file/module-scoped variables

Semicolon insertion (D, L)

semicolons are optional

when omitted, they are automatically inserted, sometimes not where intended

hard to get wrong though

Copyright ? 2012-2014 by Object Computing, Inc. (OCI).

All rights reserved.

10 - 3

JS Grievances

... Crockford¡¯s Bad Parts ...

Reserved words (L)

many aren¡¯t currently used, but reserved for possible future use

don¡¯t have to memorize them; let a lint tool warn you

Unicode (E, D)

uses UTF-16 characters, not UTF-8, and string methods expect only 2-byte characters, not 4

characters in all modern languages only require 2 bytes

typeof (Y)

typeof null === 'object' and typeof [1, 2, 3] === 'object'

Numbers (E, D)

all are represented by a double; no integer type,

but can accurately represent up to 53 bits

which is large enough for almost all uses

Copyright ? 2012-2014 by Object Computing, Inc. (OCI).

All rights reserved.

10 - 4

JS Grievances

... Crockford¡¯s Bad Parts

Arrays (E, D)

represents arrays as objects where keys are string versions of indexes

a potential performance issue; but not typically

ES6 adds typed arrays of numbers

Falsy values (Y)

false, undefined, null, 0, NaN and ""

are all treated as false in boolean contexts

everything else is truthy

== vs. === and != vs. !== (L)

short forms perform type coercion, long forms do not

eval(code) (D, L)

need to be careful about source of code

Copyright ? 2012-2014 by Object Computing, Inc. (OCI).

All rights reserved.

10 - 5

JS Grievances

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