ps-blitz-script 0.4.6

JavaScript execution for Blitz using the Boa engine
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140

//! `getComputedStyle` answers with the engine's values, not with a stub.
//!
//! Measured over a hundred-site corpus, three sites stopped on
//! `getComputedStyle is not defined`. The tempting fix is an object that
//! returns the empty string for everything, and it is worse than the error: a
//! page that reads `display` and gets `""` concludes nothing is hidden and lays
//! itself out wrongly, with nothing in the log to say why. The error at least
//! stopped loudly.
//!
//! So these tests assert real values. A stub would pass a test that only
//! checked the call did not throw, which is exactly the test not to write.

use blitz_dom::Document as _;
use blitz_script::ScriptDocument;

fn eval_string(doc: &mut ScriptDocument, code: &str) -> String {
    doc.eval(&format!("globalThis.__out = String({code});"));
    doc.eval_json("globalThis.__out")
        .ok()
        .and_then(|v| v.as_str().map(str::to_owned))
        .unwrap_or_default()
}

fn page() -> ScriptDocument {
    ScriptDocument::from_html(
        r#"<html><head><style>
             #shown { display: flex; width: 320px; height: 40px; color: rgb(1, 2, 3); }
             #gone  { display: none; }
           </style></head>
           <body style="margin:0">
             <div id="shown">visible</div>
             <div id="gone">hidden</div>
           </body></html>"#,
        blitz_dom::DocumentConfig::default(),
    )
}

/// The value distinguishes a hidden element from a shown one.
///
/// This is the assertion a stub cannot pass, and the one the failing sites
/// actually depended on.
#[test]
fn a_hidden_element_reports_display_none() {
    let mut doc = page();
    doc.execute_scripts();
    doc.inner_mut().resolve(0.0);

    let shown = eval_string(
        &mut doc,
        "getComputedStyle(document.getElementById('shown')).display",
    );
    let gone = eval_string(
        &mut doc,
        "getComputedStyle(document.getElementById('gone')).display",
    );

    assert_eq!(shown, "flex", "a shown element should report its display");
    assert_eq!(gone, "none", "a hidden element should report `none`");
    assert_ne!(
        shown, gone,
        "a stub returning one value for both is the bug"
    );
}

/// `getPropertyValue` reads the same values as property access.
#[test]
fn get_property_value_agrees_with_property_access() {
    let mut doc = page();
    doc.execute_scripts();
    doc.inner_mut().resolve(0.0);

    let direct = eval_string(
        &mut doc,
        "getComputedStyle(document.getElementById('shown')).display",
    );
    let via_getter = eval_string(
        &mut doc,
        "getComputedStyle(document.getElementById('shown')).getPropertyValue('display')",
    );

    assert_eq!(direct, "flex");
    assert_eq!(via_getter, direct);
}

/// Hyphenated names are also reachable in their camelCase spelling, because
/// scripts read `style.fontSize` as often as they ask for `font-size`.
#[test]
fn a_hyphenated_property_is_reachable_both_ways() {
    let mut doc = page();
    doc.execute_scripts();
    doc.inner_mut().resolve(0.0);

    let hyphen = eval_string(
        &mut doc,
        "getComputedStyle(document.getElementById('shown')).getPropertyValue('font-size')",
    );
    let camel = eval_string(
        &mut doc,
        "getComputedStyle(document.getElementById('shown')).fontSize",
    );

    assert!(
        hyphen.ends_with("px"),
        "font-size should be a length, got {hyphen:?}"
    );
    assert_eq!(camel, hyphen);
}

/// `width` reports the used value, not the specified one.
///
/// A page asking `getComputedStyle(el).width` wants to know how wide the box
/// ended up. `auto` is not an answer it can use.
#[test]
fn width_reports_the_used_value() {
    let mut doc = page();
    doc.execute_scripts();
    doc.inner_mut().resolve(0.0);

    let width = eval_string(
        &mut doc,
        "getComputedStyle(document.getElementById('shown')).width",
    );

    assert_eq!(width, "320px", "width should be the laid-out width");
}

/// A property outside the supported set reads as unset rather than throwing.
#[test]
fn an_unsupported_property_reads_as_empty() {
    let mut doc = page();
    doc.execute_scripts();
    doc.inner_mut().resolve(0.0);

    let value = eval_string(
        &mut doc,
        "getComputedStyle(document.getElementById('shown')).getPropertyValue('clip-path')",
    );

    assert_eq!(value, "", "an unsupported property should read as unset");
}