Converts a QGIS Expression string into a JS function.
Work in progress...
Main ussage at the moment is for qgis2web (https://github.com/tomchadwin/qgis2web) by Tom
import qgs2js
functionjs, name = qgs2js.compile("1 + 1")
# Put the functionjs and call to name in your JS string.
outputjs = functionjs
outputjs += name + "(context)"Work in progress examples
A super simple example.
var feature = {
COLA: 1,
COLB: 2,
WAT: 'Hello World'
};
var context = {
feature: feature,
variables: {}
};
function wqjr_eval_expression(context) {
// (1 + 1) * 3 + 5
var feature = context.feature;
return (((1 + 1) * 3) + 5);
}
var result = wqjr_eval_expression(context);
console.log(result);function ueun_eval_expression(context) {
// NOT var('myvar') = format('some string %1 %2', 'Hello', 'World')
var feature = context.feature;
return ! (fnc_var(['myvar'], context) == fnc_format(['some string %1 %2','Hello','World'], context)) ;
}
var result = ueun_eval_expression(context);
console.log(result);A more complicated example with columns, functions, case, and OR.
function rgpj_eval_expression(context) {
// CASE WHEN to_int(123.52) = var('myvar') THEN to_real(123) WHEN 1 + 2 = 3 THEN 2 ELSE to_int(1) END OR 2 * 2 + 5 = 4
var feature = context.feature;
function _CASE() {
if (fnc_to_int([123.52], context) == fnc_var(['myvar'], context)) {
return fnc_to_real([123], context);
}
else if ((1 + 2) == 3) {
return 2;
}
else {
return fnc_to_int([1], context);
}
};
return (_CASE() || (((2 * 2) + 5) == 4));
}
var result = rgpj_eval_expression(context);
console.log(result);Comparing columns in a case statement.
function ppwa_eval_expression(context) {
// CASE WHEN COLA = 1 THEN 1 WHEN 1 + 2 = 3 THEN 2 ELSE 3 END
var feature = context.feature;
function _CASE() {
if (feature['COLA'] == 1) {
return 1;
}
else if ((1 + 2) == 3) {
return 2;
}
else {
return 3;
}
};
return _CASE();
}
var result = ppwa_eval_expression(context);
console.log(result);QGIS will convert the expression into a AST (Abstract Syntax Tree) which makes it easy to walk down each node. We handle each node and translate it to the JS version of it.
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