Jest coverage: How can I get a total percentage of coverage?

I needed this myself, so I created a custom reporter. You need the json-summary reporter enabled in coverageReporters and then you can use this custom reporter to show the total:

const { readFile } = require('fs');
const { join } = require('path');

// Gitlab Regex: Total Coverage: (\d+\.\d+ \%)
module.exports = class CoverageReporter {
  constructor(globalConfig) {
    this.globalConfig = globalConfig;
    this.jsonSummary = join(this.globalConfig.coverageDirectory, 'coverage-summary.json');
  }
  async onRunComplete() {
    const coverage = require(this.jsonSummary);
    const totalSum = ['lines', 'statements', 'functions', 'branches']
      .map(i => coverage.total[i].pct)
      .reduce((a, b) => a + b, 0)
    const avgCoverage = totalSum / 4
    console.debug()
    console.debug('========= Total Coverage ============')
    console.debug(`Total Coverage: ${avgCoverage.toFixed(2)} %`)
    console.debug('=======================================')
  }
}

Internally jest is using Istanbul.js to report coverage and you can modify Jest's configuration with CLI arg to "text-summary" or any other alternative reporter.

jest --coverageReporters="text-summary"

text-summary output:

=============================== Coverage summary ===============================
Statements   : 100% ( 166/166 )
Branches     : 75% ( 18/24 )
Functions    : 100% ( 49/49 )
Lines        : 100% ( 161/161 )
================================================================================

Or you can write your own reporter.

Thank's to Teneff's answer, I go with the coverageReporter="json-summary".

 jest --coverage --coverageReporters="json-summary" 

This generates a coverage-summary.json file which can easily be parsed. I get the total values directly from the json:

  "total": {
    "lines": { "total": 21777, "covered": 65, "skipped": 0, "pct": 0.3 },
    "statements": { "total": 24163, "covered": 72, "skipped": 0, "pct": 0.3 },
    "functions": { "total": 5451, "covered": 16, "skipped": 0, "pct": 0.29 },
    "branches": { "total": 6178, "covered": 10, "skipped": 0, "pct": 0.16 }
  }