vega-expression

import { parse, codegen } from 'vega-expression'; interface DataItem { value: number; category: string; } // 1. Define the expression string const expressionString = "datum.value * 2 + 5"; // 2. Parse the expression into an AST const ast = parse(expressionString); console.log('Parsed AST:', JSON.stringify(ast, null, 2)); // 3. Create a code generator, specifying the field variable ('datum' in this case) // and any allowed globals/functions if needed. const generator = codegen({ fieldvar: 'datum', allowed: ['datum'], // 'datum' is an allowed variable in the expression scope // You can also provide custom functions or constants functions: () => ({ pow: (args: any[]) => `Math.pow(${args[0]}, ${args[1]})` }) }); // 4. Generate the executable code from the AST const { code, fields, globals } = generator(ast); console.log('\nGenerated Code:', code); console.log('Referenced Fields:', fields); console.log('Referenced Globals:', globals); // 5. Evaluate and use the generated function // NOTE: Using `Function` constructor is generally discouraged due to CSP issues. // For Vega runtime, `vega-interpreter` offers CSP-compliant evaluation. const evaluateExpression = new Function('datum', `return ${code};`); const sampleData: DataItem = { value: 10, category: 'A' }; const result = evaluateExpression(sampleData); console.log(`\nResult for { value: 10 } (10 * 2 + 5):`, result); // Expected: 25 const anotherData: DataItem = { value: 7, category: 'B' }; const anotherResult = evaluateExpression(anotherData); console.log(`Result for { value: 7 } (7 * 2 + 5):`, anotherResult); // Expected: 19