Looking up a position

##Loading a source map

You can construct a SourceMapLookup from a file path, a raw JSON string, or an already decoded array.

use Spatie\SourcemapsLookup\SourceMapLookup;

// From a file path (reads and decodes).
$map = SourceMapLookup::fromFile('/path/to/bundle.js.map');

// From a JSON string (for example, contents already in memory).
$map = SourceMapLookup::fromJson($json);

// From an array (for example, when you already decoded the JSON).
$map = SourceMapLookup::fromArray($data);

Construction is cheap. The raw mappings string is stored but not parsed until you actually call lookup(). Only the lines you touch are decoded.

##Looking up a position

$position = $map->lookup(line: 42, column: 17);

$line is 1-based (matches stack trace conventions). $column is 0-based (matches the Source Map v3 spec and browsers).

The call returns a Position object, or null if no mapping applies for that coordinate (see below).

The lookup returns the last mapping on the given line whose generated column is less than or equal to $column, following the standard Source Map v3 lookup semantics.

##The Position object

readonly class Position
{
    public int $sourceLine;          // 1-based
    public int $sourceColumn;        // 0-based
    public ?string $sourceFileName;  // resolved with sourceRoot when present, null if spec-null
    public int $sourceFileIndex;     // index into sources[] / sourcesContent[]
    public ?string $name;            // symbol name, or null for 4-field mappings
}

When the source map has a sourceRoot, sourceFileName is returned as sourceRoot . sources[i]. The package does not further resolve relative paths. If you need absolute URLs, do that in your caller.

##When lookup() returns null

lookup() returns null in three cases, all of which mean "no original source for this position":

1. No mappings exist for the requested line.
2. No mapping on the line has generatedColumn <= $column.
3. The best matching mapping is a 1-field (unmapped) segment. Per the spec, this explicitly marks the generated column as intentionally unmapped.

You should treat all three the same way. There is simply no known original source for that frame.