projectContinuousExcerpt

KIT · function · Runtime value

Project a continuous excerpt of a body by binary-searching the longest prefix that fits.

Binary-search a continuous prefix and keep an existing surrogate pair intact. render receives the prefix length, not the text, so the caller decides how the excerpt is framed.

Import

TypeScript

import { projectContinuousExcerpt } from '@jangts/agent-core/kits/projection';

JavaScript

import { projectContinuousExcerpt } from '@jangts/agent-core/kits/projection';

Other public entry points:@jangts/agent-core/types, @jangts/agent-core/kits/projection, @jangts/agent-core/kits.

Definition

Call

projectContinuousExcerpt(body: string, limit: number, render: (length: number) => string): ContentProjection | undefined

Project a continuous excerpt of a body by binary-searching the longest prefix that fits.

Binary-search a continuous prefix and keep an existing surrogate pair intact. render receives the prefix length, not the text, so the caller decides how the excerpt is framed.

Parameter	Type	Passing	Description
body	string	Required	—
limit	number	Required	—
render	(length: number) => string	Required	—

Returns: ContentProjection \| undefined.

Optional shapes of Return value: choose one shape; required fields for each branch are listed separately.

Branch 1

undefined

Branch 2

Field	Type	Required	Description
text	string	Required	Read-only. Rendered text that fits the requested budget.
truncated	boolean	Required	Read-only. True when anything was shortened or replaced by the fallback.

Examples

• Projection: project content under a budget: Shorten text first, then reduce entries; source data, projection result, and budget are explicitly separated by the App.

Prepare compact JSON for the same query result

Beginner · Node.js

TypeScript

import { Projection } from '@jangts/agent-core/kits/projection';
const projection = Projection.defineContentProjection({
  counts: [10, 3, 1], lengths: [200, 80, 20],
  render: value => JSON.stringify(value), fallback: () => '{}',
});
const result = projection.project({ value: { items: [{ title: '配置说明', body: '正文'.repeat(100) }] }, maxChars: 120 });
console.log(result.text, result.truncated);

JavaScript

import { Projection } from '@jangts/agent-core/kits/projection';
const projection = Projection.defineContentProjection({
    counts: [10, 3, 1], lengths: [200, 80, 20],
    render: value => JSON.stringify(value), fallback: () => '{}',
});
const result = projection.project({ value: { items: [{ title: '配置说明', body: '正文'.repeat(100) }] }, maxChars: 120 });
console.log(result.text, result.truncated);

Remove private fields from the same data, then project under budget

Configuration · Node.js

TypeScript

import { Projection } from '@jangts/agent-core/kits/projection';
const tree = Projection.defineTreeProjection({
  maxDepth: 4,
  visitRecord(record) { delete record.privateNote; },
});
const source = { items: [{ title: '配置说明', body: '正文'.repeat(100), privateNote: '不向模型提供' }] };
// 调用者明确选择副本所有权；visitor 不会碰原记录。
const publicData = tree.visit(structuredClone(source), undefined);
const compact = Projection.defineContentProjection({ counts: [10, 3, 1], lengths: [200, 80, 20], render: JSON.stringify, fallback: () => '{}' });
console.log(compact.project({ value: publicData, maxChars: 120 }));

JavaScript

import { Projection } from '@jangts/agent-core/kits/projection';
const tree = Projection.defineTreeProjection({
    maxDepth: 4,
    visitRecord(record) { delete record.privateNote; },
});
const source = { items: [{ title: '配置说明', body: '正文'.repeat(100), privateNote: '不向模型提供' }] };
// 调用者明确选择副本所有权；visitor 不会碰原记录。
const publicData = tree.visit(structuredClone(source), undefined);
const compact = Projection.defineContentProjection({ counts: [10, 3, 1], lengths: [200, 80, 20], render: JSON.stringify, fallback: () => '{}' });
console.log(compact.project({ value: publicData, maxChars: 120 }));

Keep continuous body text instead of splitting paragraphs

Extension · Node.js

The output length of render must grow monotonically with the prefix length for the binary search to be meaningful.

TypeScript

import { Projection } from '@jangts/agent-core/kits/projection';
const body = '一段连续的资料正文。'.repeat(100);
const excerpt = Projection.projectContinuousExcerpt(body, 120, length => JSON.stringify({ excerpt: body.slice(0, length) }));
if (excerpt) console.log(JSON.parse(excerpt.text));

JavaScript

import { Projection } from '@jangts/agent-core/kits/projection';
const body = '一段连续的资料正文。'.repeat(100);
const excerpt = Projection.projectContinuousExcerpt(body, 120, length => JSON.stringify({ excerpt: body.slice(0, length) }));
if (excerpt)
    console.log(JSON.parse(excerpt.text));

Related policy source

• Reduction order and tree traversal

Related definitions

• ContentProjection